[c++] Some use_current_domain unit-test/feature-flag teardown, part 4 of 4

[johnkerl]

Issue and/or context: As tracked on issue #2407 / [sc-51048]. Also #3273.

Note that the intended Python and R API changes are all agreed on and finalized as described in #2407.

Changes:

Notes for Reviewer:

This is fourth in a series of PRs. While the changes are trivial, the line-count can be intimidating when it's attempted all at once.

Stacked on #3371

The line count is big but mostly whitespace. Suggestion: hide whitespace when reviewing:
https://github.com/single-cell-data/TileDB-SOMA/pull/3372/files?diff=split&w=1

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.15%. Comparing base (937b43d) to head (8bfc49a).
Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #3372       +/-   ##
===========================================
+ Coverage   66.94%   86.15%   +19.20%     
===========================================
  Files         139       55       -84     
  Lines       17727     6094    -11633     
  Branches     1063        0     -1063     
===========================================
- Hits        11868     5250     -6618     
+ Misses       5483      844     -4639     
+ Partials      376        0      -376     

Flag	Coverage Δ
libtiledbsoma	?
python	86.15% <ø> (+0.09%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
python_api	86.15% <ø> (+0.09%)	⬆️
libtiledbsoma	∅ <ø> (∅)

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