CI: Check private function not used across modules
- [x] xref https://github.com/pandas-dev/pandas/pull/32942#issuecomment-609893282
- [ ] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

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

* In the file [`scripts/validate_unwanted_patterns.py`](https://github.com/pandas-dev/pandas/blob/286e49488bf748f0eb563c7e9d58e53e944c8c78/scripts/validate_unwanted_patterns.py):

> [Line 154:9](https://github.com/pandas-dev/pandas/blob/286e49488bf748f0eb563c7e9d58e53e944c8c78/scripts/validate_unwanted_patterns.py#L154): [E266](https://duckduckgo.com/?q=pep8%20E266) too many leading '#' for block comment

 @MomIsBestFriend can i convince you to pick this and/or #33394 back up?  I found myself manually tracking down incorrectly-private functions today, would be nice to avoid that need.