TST/CLN: Old timezone issues PT3
- [x] closes #13783
- [x] closes #12619
- [x] closes #15522
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

xref #21612 and #21491, last of the cleanup of older timezone issues
