32380 deprecate squeeze in groupby
- [x] closes #32380
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

I deprecated the squeeze keyword. I think I got every points this keyword was used. 
I hope that I considered every point necessary to deprecate a keyword. I tried to use other points were a keyword was deprecated as example.

Hello @phofl! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:









There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2020-05-22 13:44:41 UTC We will still need a whatsnew entry for this (the one you had in a prior commit was good iirc) @mroeschke  I have added the whats new entry. Looks good. Just need to merge master to fix the merge conflict and address @WillAyd's comment.  > 
> 
> Looks good. Just need to merge master to fix the merge conflict and address @WillAyd's comment.

Done Looks good. Can you update. > 
> 
> Looks good. Can you update.

Done Ci failure should be unrelated - can you merge master and repush? thanks @phofl very nice.