CLN: followons to refactor of series/test_indexing.py

[jreback]

xref #18614

• remove the classes, IOW make all of the tests at function level. This will require removing the setup_method and making fixtures for this. (Moving tests in series/indexing to fixtures (#20014.1) #20034)
• some tests need to be moved around a bit, IOW we want to move tests out of test_indexing.py (the new one), so appropriate places (e.g. .drop should be in alter_axes). (TST: series/indexing tests parameterization + moving test methods #20059)
• want to parameterize things (e.g. anything with loops) (TST: series/indexing tests parameterization + moving test methods #20059)

any/all of these can be separate PRs.

[almaleksia]

@jreback I will start working on it if you don't mind :)