CLN: Remove unused functions/variables

[twoertwein]

Found by pyright's reportUnused*.

Unused functions/variables are not directly related to typing, but pyright warns about these cases because it is asked to do unnecessary work.

[jreback]

looks good, some failures

[twoertwein]

A few of the private functions are only called by tests which caused them to fail. The only failing test now is codecov/patch for some reason.

[jreback]

can you rebase

[twoertwein]

@jreback rebased & green

[jreback]

thanks @twoertwein did you need to turn on a pyright option to have this reported? e.g. can we have it always run? (or is it expensive)

[twoertwein]

I didn't turn them one because we have false-positives. We "exclude" pandas/tests - if we were to "ignore" pandas/tests, we probaly wouldn't have these false-positives anymore but pyright might be 30-50s slower if it has to work through the mostly un-typed tests.

The four options from pyright are:

• reportUnusedClass: is only "offended" in one file (pickle compat) where a private class is refernced using only a string. We could disable reportUnusedClass for this file using with a comment at the top of the file.
• reportUnusedFunction: needs a discussion whether these private functions should either be moved (often they are used only one time, but defiend in a different file) or made "public" (at least remove the leading "_")
• reportUnusedImport: could probably be enabled if __all__ or redundant import were used (main "offenders" are the api.py files)
• reportUnusedVariable: needs consensus to start unused variables with _ (flake8-bugbear has the same rules but it is not enabled because it is "controversial").