Add  `remove_columns` to `IterableDataset ` 
Hi ! Good idea :)
If you are interested in contributing, feel free to give it a try and open a Pull Request. Also let me know if I can help you with this or if you have questions
**Is your feature request related to a problem? Please describe.**
A clear and concise description of what the problem is.

```python
from datasets import load_dataset
dataset = load_dataset("c4", 'realnewslike', streaming =True, split='train')
dataset = dataset.remove_columns('url')
```
```
AttributeError: 'IterableDataset' object has no attribute 'remove_columns'
```

**Describe the solution you'd like**

It would be nice to have `.remove_columns()` to match the `Datasets` api. 


**Describe alternatives you've considered**

This can be done with a single call to `.map()`, 

I can try to help add this. 🤗