Remove some dead code

[fingolfin]

Note that the functions related to involutions are all in orb, without the 'RECOG.' prefix.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.51%. Comparing base (e1c7faf) to head (29de129).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #513   +/-   ##
=======================================
  Coverage   86.51%   86.51%           
=======================================
  Files          45       45           
  Lines       19262    19262           
=======================================
  Hits        16665    16665           
  Misses       2597     2597           

Files with missing lines	Coverage Δ
gap/projective/tensor.gi	59.43% <ø> (ø)

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[fingolfin]

@Till-Eisen please have a look if you see anything in there you feel could still be useful (don't worry, though: even if you miss something, it's of course all still in the history)

[Till-Eisen]

@fingolfin Yes, I have.
RECOG.FindTensorOtherFactor is clearly incomplete: it has no return statement other than fail (and more is missing), so it looks like it was only implemented halfway.
RECOG.VerifyTensorDecomposition looks like it could be useful, but it's not called anywhere either...
And the rest is related to involutions, i.e. in orb as you said.