MNT: cleanup test data

[bsipocz]

I was running into some discrepancies while investigating the current CI failure (#2250 (comment)).

I've left alone two recently added, but yet unused test files as adding more testing is in the near future plans for that module (#2328 (comment))

[bsipocz]

There are more to come, these are only the ones picked up by missing from the MANIFEST collection.

[bsipocz]

OK, this is ready now. I haven't run remote tests on these changes, but we ideally should do that before merging to see nothing got broken due to these clearups.

[bsipocz]

I've run the remote tests and none of them seems to be new and due to the changes in this PR (it's a bit difficult to say it for certain as the test suite runs for ~2hrs and has 41 failures, some of which are temporary flukes, etc.)

[codecov]

Codecov Report

Merging #2342 (e51d3ee) into main (c081ee4) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #2342   +/-   ##
=======================================
  Coverage   63.40%   63.40%           
=======================================
  Files         131      131           
  Lines       17044    17044           
=======================================
  Hits        10807    10807           
  Misses       6237     6237           

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