[DOC]: Improve drop docs
- [x] xref#36293

Improved the docstring a bit in case of multi-index and no level given.
Before merging we should address the inconsistency betweend unique MultiIndexes, where something like df.drop(index="test") works and non unique MultiIndexes, where the same does not work (#36293) This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this. I dont' think we actually want to change the docks, rather fix the bug. closing.