Remove properties from groupby whitelists
This is a small piece broken off of #17179, keeping a modicum of forward momentum going.

- [ ] closes #xxxx
- [ ] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

We discussed this back in #17179.  Generating these methods is several distinct types of bad, hides bugs like #17608. generating these the current method I agree. However using a real function definition is the correct methodology here; see how we do generated functions in https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L6568

all with proper doc-strings and such.