Make testinstall work with gap --bare

[fingolfin]

• provide a better TransitiveGroupsAvailable fallback
• remove a bunch of SmallGroup and IdGroup uses
• remove tst/testbugfix/2005-05-03-t00070.tst (an equivalent test was added to the smallgrp package recently)
• modify some .tst file to run parts only if certain packages are available, via #@if IsPackageMarkedForLoading(...)
• don't load ctbllib (and all its dependencies) in ctblmaps.tst

Together with #6353 this is meant to resolve issue #6346, once it is done, which is not.

TODO:

• add a CI test which runs testinstall with --bare
• fix remaining issue in .tst files (i.e. need more #@if IsPackageMarkedForLoading(...) guards etc)

[codecov]

Codecov Report

❌ Patch coverage is 90.90909% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 74.51%. Comparing base (7889216) to head (a3ea9e6).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
lib/grpnames.gi	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6354      +/-   ##
==========================================
- Coverage   76.11%   74.51%   -1.60%     
==========================================
  Files         683      676       -7     
  Lines      292488   288377    -4111     
  Branches     8644     8268     -376     
==========================================
- Hits       222631   214898    -7733     
- Misses      68033    71693    +3660     
+ Partials     1824     1786      -38     

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