Remove Python 3.9 __subclasscheck__ workaround

[ryan-williams]

This code dates to Feb '23, doesn't seem to be necessary for tests/CI (including Typeguard and mypy) to pass, and seems to be causing issues in TileDB-SOMA CI (e.g. single-cell-data/TileDB-SOMA#3246).

Here's a sweep of:

• Python: { 3.9.10, 3.9.19 3.12.7 }
• SOMA: { main, rw/slc (this branch) }
• Typeguard: { 4.2.1, 4.3.0, 4.4.0 }
• Single test case: test_dataframe_index_columns.py::test_types_no_errors[soma_joinid-py-slice-index_column_names4-domain4-coords4-expecteds4] (started failing on Python 3.9, ca. typeguard#496 / 4.4.0)

Notes:

• Typeguard 4.2.1: everything passes. Typeguard added more checks and fixes in 4.3.0 and 4.4.0…
• Typeguard 4.3.0: everything fails, errors refer to __orig_bases__.
  • There was discussion of this on #222, ultimately typeguard#496 was the fix, which landed in 4.4.0.
• Typeguard 4.4.0: Python 3.9 fails on main, everything passes on this branch.

I've been unable to find a situation where the __subclasscheck__ block here is necessary; my best guess (and from discussing with @jp-dark) is that it was relevant to older Typeguard versions (TileDB-SOMA would have been on 2.x when this code was added, in Feb '23). I've locally tested Python versions 3.9.{4,7,10,11,13,19}, they all seem to have the same behavior (failure with Typeguard 4.4.0 and this code present, OK without this code, OK on 4.2.1 with and without this code).

Here's TileDB-SOMA CI passing when pointed at this branch (single-cell-data/TileDB-SOMA#3250).

[johnkerl]

🚀