DEPR: Remove Series.compress
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

As noted in https://github.com/pandas-dev/pandas/issues/6581, sounds like we are okay breaking compatibility with `np.compress`
thanks @mroeschke 