fix: remove unused keyword arg

[agoose77]

#1968 added the redundant return_simplified argument to ak.transform. I missed it in my initial review, but it doesn't do anything and should be removed. I think we can do this immediately; the option isn't documented, and doesn't do anything.

[codecov]

Codecov Report

Merging #2046 (8e2f4e1) into main (64377c1) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

Impacted Files	Coverage Δ
src/awkward/operations/ak_transform.py	91.30% <ø> (ø)

[jpivarski]

Oops!

You're right: that's a relic of a partial implementation. At first, return_array and return_simplified were to be two booleans, but two booleans have 4 possible values and only 3 of them would have been meaningful, so I combined them into a single enumerated argument, return_value.

The return_simplified is left over from having implemented it the one way, changing my mind, and implementing it the other way without completely cleaning up.

It is possible for someone to depend on it the same way as the last change in arguments: someone could be uselessly passing an argument through a wrapper of transform, which would then fail if an argument of this name disappears. However, this is much less likely than in the previous case, since transform is a new function and it's too low-level to be a dask-awkward function. So I agree that we can try silently removing it.

I approve this PR for merging.