Avoid some uses of IdGroup

[fingolfin]

We should keep uses of smallgrp/primgrp/transgrp to a minimum (see #2434).

Also, the uses here directly affects some package test suites, as revealed by my experiments at gap-system/PackageDistro#1183

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.60%. Comparing base (22d51cc) to head (788b6b6).
⚠️ Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
grp/simple.gi	44.44%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6343      +/-   ##
==========================================
+ Coverage   78.56%   78.60%   +0.03%     
==========================================
  Files         684      684              
  Lines      292844   292699     -145     
  Branches     8657     8660       +3     
==========================================
+ Hits       230070   230073       +3     
+ Misses      60964    60814     -150     
- Partials     1810     1812       +2     

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[ThomasBreuer]

We should keep uses of smallgrp/primgrp/transgrp to a minimum

Is this a good idea?

I think it is very useful to talk about (the isomorphism type of) a group in terms of some identifier.
When two persons (or papers or databases) describe a group in different ways then one has to work in order to verify that it is in fact the same group.
(This is not an issue for the very small groups that occur in this pull request.)

[fingolfin]

I agree that we shouldn't just replace all uses of IdGroup. That's why I wrote "keep it to a minimum", not "eliminate it entirely": we use it were we must / where it is useful, but we avoid it where there are trivial alternatives. I think in the cases I deal with here, the replacements are fine, especially because there are usually also comments next to them that explains what's going on. I can add some more to the others to make it even clearer

[fingolfin]

@ThomasBreuer OK to merge this? I sympathize with the wish to have some "rules" somewhere on this, but I don't know where to put those; and honestly, there are countless more such things were some people know to avoid certain things (e.g. immediate methods) but it is not codified anywhere. And here I am not even sure what the "rule" should be: I don't mean to forbid IdGroup entirely, it's just that in the cases I modify here, it was unnecessary, and it blocks testing a couple packages with --bare. But it's not as if a "rule" was broken; and if someone later adds back some uses of IdGroup, the worst that'll happen is that some CI test in the package distro fails, and we'll deal with it.

Anyway, I also filed #6346