Multiindex drop doc improvement
- [ ] closes #43793 
- [ ] tests added / passed - N/A
- [ ] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them - N/A
- [ ] Improved documentation for ``DataFrame.drop``

thanks @juliandwain 