CLN: Remove Ops Mixin from pandas/tests/base
11 PRs later, the moment has finally come: closes #23877 🎉 

- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`



thanks @SaturnFromTitan very nice!

ok next up would be to start splitting things out of test_ops to better named modules.