CLN: MultiIndex.drop_duplicates
I think there is no reason why `MultiIndex` overwrites `drop_duplicates` from `Index`:

- Both implementations do exactly the same
- Both implementations have exactly the same type annotations
- `MultiIndex.drop_duplicates` does not have a doc-string

There are a few more methods (`set_names`, `rename`) but in those cases, the annotations might actually be different.
Thanks @twoertwein 