[python] Update comments, remove unused test params

[ryan-williams]

Issue and/or context: #2829, #2804, #2868

Changes:

• Tests introduced in [python] Ingest/outgest round-trip improvements #2804 included configurable outgest_default_index_name and outgest_fallback_index_name fields, that were never set to non-default values. Removing them here, to avoid confusion.
• Other comment updates / typo fixes

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.84%. Comparing base (190e479) to head (2e5b53a).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2873      +/-   ##
==========================================
+ Coverage   89.69%   89.84%   +0.15%     
==========================================
  Files          37       37              
  Lines        3940     3940              
==========================================
+ Hits         3534     3540       +6     
+ Misses        406      400       -6     

Flag	Coverage Δ
python	89.84% <ø> (+0.15%)	⬆️

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Components	Coverage Δ
python_api	89.84% <ø> (+0.15%)	⬆️
libtiledbsoma	∅ <ø> (∅)

[johnkerl]

🚢