Revert PreImagesRepresentative for IsLinearActionHomomorphism

[fingolfin]

This was changed in PR #6232 but the change causes the recog test suite to fail. This looks like a symptom of other deeper issues, but until we can understand and fix this better, let's be pragmatic and revert this for now.

This is being tracked in issue #6389; I propose not to close that right now, though, because we still want to understand the deeper issue better.

[ThomasBreuer]

I expect that we have to revert all changes related to matrix groups consisting of matrix objects.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.06%. Comparing base (403924c) to head (f9dece2).

❗ There is a different number of reports uploaded between BASE (403924c) and HEAD (f9dece2). Click for more details.

HEAD has 18 uploads less than BASE

Flag	BASE (403924c)	HEAD (f9dece2)
	20	2

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #6395       +/-   ##
===========================================
- Coverage   78.67%   60.06%   -18.62%     
===========================================
  Files         683      635       -48     
  Lines      292942   252779    -40163     
  Branches     8658     7461     -1197     
===========================================
- Hits       230485   151825    -78660     
- Misses      60638    98967    +38329     
- Partials     1819     1987      +168     

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