accelerator refactor - remove legacy tests that cannot pass

[awaelchli]

What does this PR do?

Remove tests in legacy folder that cannot pass anymore after the refactor.
These tests were moved and adapted in #5743.
This PR should be merged immediately before #5743

cc @justusschock @Borda

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[codecov]

Codecov Report

Merging #5849 (b5e1f6a) into release/1.2-dev (4d2b13f) will decrease coverage by 0%.
The diff coverage is n/a.

@@               Coverage Diff                @@
##           release/1.2-dev   #5849    +/-   ##
================================================
- Coverage               88%     88%    -0%     
================================================
  Files                  181     181            
  Lines                12928   12759   -169     
================================================
- Hits                 11426   11229   -197     
- Misses                1502    1530    +28     

[justusschock]

Just some conflicts to resolve :)