map() function removes columns when input_columns is not None
## Describe the bug
The map function, removes features from the dataset that are not present in the _input_columns_ list of columns, despite the columns being removed not mentioned in the _remove_columns_ argument.
## Steps to reproduce the bug
```python
from datasets import Dataset
ds = Dataset.from_dict({"a" : [1,2,3],"b" : [0,1,0], "c" : [2,4,5]})

def double(x,y):
  x = x*2
  y = y*2
  return {"d" : x, "e" : y}

ds.map(double, input_columns=["a","c"])
```

## Expected results
```
Dataset({
    features: ['a', 'b', 'c', 'd', 'e'],
    num_rows: 3
})
```
## Actual results
```
Dataset({
    features: ['a', 'c', 'd', 'e'],
    num_rows: 3
})
```

In this specific example feature **b** should not be removed.

## Environment info
<!-- You can run the command `datasets-cli env` and copy-and-paste its output below. -->
- `datasets` version: 2.4.0
- Platform: linux (colab)
- Python version: 3.7.13
- PyArrow version: 6.0.1
