We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
Remove SCRAPY_SELECTORS_BACKEND from scrapy.settings.deprecated
There is no trace of `SCRAPY_SELECTORS_BACKEND` in the code anymore, so that line should go.

It would be a good chance to review the rest of the lines in that file, some others may be worth removing as well.

Related to https://github.com/scrapy/scrapy/issues/4356

--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `scrapy/settings/deprecated.py`
Content:
```
1 import warnings
2 from scrapy.exceptions import ScrapyDeprecationWarning
3 
4 DEPRECATED_SETTINGS = [
5     ('TRACK_REFS', 'no longer needed (trackref is always enabled)'),
6     ('RESPONSE_CLASSES', 'no longer supported'),
7     ('DEFAULT_RESPONSE_ENCODING', 'no longer supported'),
8     ('BOT_VERSION', 'no longer used (user agent defaults to Scrapy now)'),
9     ('ENCODING_ALIASES', 'no longer needed (encoding discovery uses w3lib now)'),
10     ('STATS_ENABLED', 'no longer supported (change STATS_CLASS instead)'),
11     ('SQLITE_DB', 'no longer supported'),
12     ('SELECTORS_BACKEND', 'use SCRAPY_SELECTORS_BACKEND environment variable instead'),
13     ('AUTOTHROTTLE_MIN_DOWNLOAD_DELAY', 'use DOWNLOAD_DELAY instead'),
14     ('AUTOTHROTTLE_MAX_CONCURRENCY', 'use CONCURRENT_REQUESTS_PER_DOMAIN instead'),
15     ('AUTOTHROTTLE_MAX_CONCURRENCY', 'use CONCURRENT_REQUESTS_PER_DOMAIN instead'),
16     ('REDIRECT_MAX_METAREFRESH_DELAY', 'use METAREFRESH_MAXDELAY instead'),
17     ('LOG_UNSERIALIZABLE_REQUESTS', 'use SCHEDULER_DEBUG instead'),
18 ]
19 
20 
21 def check_deprecated_settings(settings):
22     deprecated = [x for x in DEPRECATED_SETTINGS if settings[x[0]] is not None]
23     if deprecated:
24         msg = "You are using the following settings which are deprecated or obsolete"
25         msg += " (ask scrapy-users@googlegroups.com for alternatives):"
26         msg = msg + "\n    " + "\n    ".join("%s: %s" % x for x in deprecated)
27         warnings.warn(msg, ScrapyDeprecationWarning)
28
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/scrapy/settings/deprecated.py b/scrapy/settings/deprecated.py
--- a/scrapy/settings/deprecated.py
+++ b/scrapy/settings/deprecated.py
@@ -9,10 +9,8 @@
     ('ENCODING_ALIASES', 'no longer needed (encoding discovery uses w3lib now)'),
     ('STATS_ENABLED', 'no longer supported (change STATS_CLASS instead)'),
     ('SQLITE_DB', 'no longer supported'),
-    ('SELECTORS_BACKEND', 'use SCRAPY_SELECTORS_BACKEND environment variable instead'),
     ('AUTOTHROTTLE_MIN_DOWNLOAD_DELAY', 'use DOWNLOAD_DELAY instead'),
     ('AUTOTHROTTLE_MAX_CONCURRENCY', 'use CONCURRENT_REQUESTS_PER_DOMAIN instead'),
-    ('AUTOTHROTTLE_MAX_CONCURRENCY', 'use CONCURRENT_REQUESTS_PER_DOMAIN instead'),
     ('REDIRECT_MAX_METAREFRESH_DELAY', 'use METAREFRESH_MAXDELAY instead'),
     ('LOG_UNSERIALIZABLE_REQUESTS', 'use SCHEDULER_DEBUG instead'),
 ]

{"golden_diff": "diff --git a/scrapy/settings/deprecated.py b/scrapy/settings/deprecated.py\n--- a/scrapy/settings/deprecated.py\n+++ b/scrapy/settings/deprecated.py\n@@ -9,10 +9,8 @@\n     ('ENCODING_ALIASES', 'no longer needed (encoding discovery uses w3lib now)'),\n     ('STATS_ENABLED', 'no longer supported (change STATS_CLASS instead)'),\n     ('SQLITE_DB', 'no longer supported'),\n-    ('SELECTORS_BACKEND', 'use SCRAPY_SELECTORS_BACKEND environment variable instead'),\n     ('AUTOTHROTTLE_MIN_DOWNLOAD_DELAY', 'use DOWNLOAD_DELAY instead'),\n     ('AUTOTHROTTLE_MAX_CONCURRENCY', 'use CONCURRENT_REQUESTS_PER_DOMAIN instead'),\n-    ('AUTOTHROTTLE_MAX_CONCURRENCY', 'use CONCURRENT_REQUESTS_PER_DOMAIN instead'),\n     ('REDIRECT_MAX_METAREFRESH_DELAY', 'use METAREFRESH_MAXDELAY instead'),\n     ('LOG_UNSERIALIZABLE_REQUESTS', 'use SCHEDULER_DEBUG instead'),\n ]\n", "issue": "Remove SCRAPY_SELECTORS_BACKEND from scrapy.settings.deprecated\nThere is no trace of `SCRAPY_SELECTORS_BACKEND` in the code anymore, so that line should go.\r\n\r\nIt would be a good chance to review the rest of the lines in that file, some others may be worth removing as well.\r\n\r\nRelated to https://github.com/scrapy/scrapy/issues/4356\n", "before_files": [{"content": "import warnings\nfrom scrapy.exceptions import ScrapyDeprecationWarning\n\nDEPRECATED_SETTINGS = [\n    ('TRACK_REFS', 'no longer needed (trackref is always enabled)'),\n    ('RESPONSE_CLASSES', 'no longer supported'),\n    ('DEFAULT_RESPONSE_ENCODING', 'no longer supported'),\n    ('BOT_VERSION', 'no longer used (user agent defaults to Scrapy now)'),\n    ('ENCODING_ALIASES', 'no longer needed (encoding discovery uses w3lib now)'),\n    ('STATS_ENABLED', 'no longer supported (change STATS_CLASS instead)'),\n    ('SQLITE_DB', 'no longer supported'),\n    ('SELECTORS_BACKEND', 'use SCRAPY_SELECTORS_BACKEND environment variable instead'),\n    ('AUTOTHROTTLE_MIN_DOWNLOAD_DELAY', 'use DOWNLOAD_DELAY instead'),\n    ('AUTOTHROTTLE_MAX_CONCURRENCY', 'use CONCURRENT_REQUESTS_PER_DOMAIN instead'),\n    ('AUTOTHROTTLE_MAX_CONCURRENCY', 'use CONCURRENT_REQUESTS_PER_DOMAIN instead'),\n    ('REDIRECT_MAX_METAREFRESH_DELAY', 'use METAREFRESH_MAXDELAY instead'),\n    ('LOG_UNSERIALIZABLE_REQUESTS', 'use SCHEDULER_DEBUG instead'),\n]\n\n\ndef check_deprecated_settings(settings):\n    deprecated = [x for x in DEPRECATED_SETTINGS if settings[x[0]] is not None]\n    if deprecated:\n        msg = \"You are using the following settings which are deprecated or obsolete\"\n        msg += \" (ask scrapy-users@googlegroups.com for alternatives):\"\n        msg = msg + \"\\n    \" + \"\\n    \".join(\"%s: %s\" % x for x in deprecated)\n        warnings.warn(msg, ScrapyDeprecationWarning)\n", "path": "scrapy/settings/deprecated.py"}], "after_files": [{"content": "import warnings\nfrom scrapy.exceptions import ScrapyDeprecationWarning\n\nDEPRECATED_SETTINGS = [\n    ('TRACK_REFS', 'no longer needed (trackref is always enabled)'),\n    ('RESPONSE_CLASSES', 'no longer supported'),\n    ('DEFAULT_RESPONSE_ENCODING', 'no longer supported'),\n    ('BOT_VERSION', 'no longer used (user agent defaults to Scrapy now)'),\n    ('ENCODING_ALIASES', 'no longer needed (encoding discovery uses w3lib now)'),\n    ('STATS_ENABLED', 'no longer supported (change STATS_CLASS instead)'),\n    ('SQLITE_DB', 'no longer supported'),\n    ('AUTOTHROTTLE_MIN_DOWNLOAD_DELAY', 'use DOWNLOAD_DELAY instead'),\n    ('AUTOTHROTTLE_MAX_CONCURRENCY', 'use CONCURRENT_REQUESTS_PER_DOMAIN instead'),\n    ('REDIRECT_MAX_METAREFRESH_DELAY', 'use METAREFRESH_MAXDELAY instead'),\n    ('LOG_UNSERIALIZABLE_REQUESTS', 'use SCHEDULER_DEBUG instead'),\n]\n\n\ndef check_deprecated_settings(settings):\n    deprecated = [x for x in DEPRECATED_SETTINGS if settings[x[0]] is not None]\n    if deprecated:\n        msg = \"You are using the following settings which are deprecated or obsolete\"\n        msg += \" (ask scrapy-users@googlegroups.com for alternatives):\"\n        msg = msg + \"\\n    \" + \"\\n    \".join(\"%s: %s\" % x for x in deprecated)\n        warnings.warn(msg, ScrapyDeprecationWarning)\n", "path": "scrapy/settings/deprecated.py"}]}