Ensure more tests pass with gap --bare

[fingolfin]

• 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

Extracted from PR #6346

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.54%. Comparing base (4e3501f) to head (59b394e).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6387      +/-   ##
==========================================
- Coverage   78.69%   74.54%   -4.15%     
==========================================
  Files         684      676       -8     
  Lines      292902   288538    -4364     
  Branches     8665     8271     -394     
==========================================
- Hits       230506   215103   -15403     
- Misses      60575    71642   +11067     
+ Partials     1821     1793      -28     

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