CLN: simplify _setitem_with_indexer
The MultiIndex check it is doing is unnecessary for positional indexing.

Other things being cleaned up here appear to be remnants from Panel
Now you have been working with `_setitem_with_indexer`, could you add a docstring for it explaining what the scope of this function is (eg only used for positional indexing?) > could you add a docstring for it explaining what the scope of this function is (

good idea im of mixed mind on adding a docstring at the moment, because there is a big gap between what the method does vs what it is supposed to do. Even trying to write down a bit what you know about what it is supposed to do and what it actually does (what led you to previous comment) is useful IMO; it doesn't need to be a perfectly standard formatted docstring lgtm needs a rebase rebased+green @jorisvandenbossche gentle ping Thanks!