Remove unused code (rational classes of perm groups)

[fingolfin]

This removes some code that was unused since at least July 2005. Back then, @hulpke commented it out in the CVS repository. Two relevant quotes by him:

Date:   2005-07-12 14:42:03 +0000

    Disabled old rational classes code, new code uses conjugacy classes. AH

and

Date:   2005-08-06 12:55:14 +0000

    Rational classes fused from classes remember rationality.
    Further removal of old RationalClasses code that seems to be broken. AH

Based on some comments in the code, as well as "git blame", I think this code was originally written by Heiko Theißen. Perhaps it is meant to be faster for computing rational classes of perm groups -- but the fact that it hasn't been used for over a decade leads me to think we are better of removing it (I spent some time today trying to understand parts of this code, until I figured out it wasn't actually used).

If anybody wants to resurrect and fix it in the future: It'll still be available in the history... :)

[codecov-io]

Current coverage is 49.13% (diff: 100%)

Merging #886 into master will increase coverage by 0.06%

@@             master       #886   diff @@
==========================================
  Files           422        422          
  Lines        228711     228396   -315   
  Methods        3447       3447          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits         112224     112227     +3   
+ Misses       116487     116169   -318   
  Partials          0          0          

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[hulpke]

@fingolfin Thank you -- the code (which is based on a paper by Butler, and on Heiko's diploma thesis) was intendd to be faster. Code degradation over 10 years led to problems .
The commenting-out was a "CVS style" solution as it is harder to get back to old versions. Removing the code is the right choice.

[olexandr-konovalov]

@fingolfin thanks! Deleted code is debugged code :)

[fingolfin]

In some very limited tests I made, the removed code was actually slower than what we have now.