API: remove dropped multilevel index from levels (GH: #34097)
- [x] closes #34097
- [ ] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

closing this. We do not automatically recalcualate the levels on indexing. This is an implementation details. The original issue is won't fix. All that said wouldn't be averse to perf enhancements generally.