CLN cleanup stale code in when reducing a class

[pierreglaser]

As a consequence of #262, I think some past workarounds used when saving dynamic classes can be removed. All tests seem to pass.

[codecov]

Codecov Report

Merging #271 into master will decrease coverage by 0.15%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #271      +/-   ##
==========================================
- Coverage   89.35%   89.19%   -0.16%     
==========================================
  Files           1        1              
  Lines         620      611       -9     
  Branches      131      127       -4     
==========================================
- Hits          554      545       -9     
  Misses         43       43              
  Partials       23       23

Impacted Files	Coverage Δ
cloudpickle/cloudpickle.py	89.19% <ø> (-0.16%)	⬇️

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[ogrisel]

Thanks very much @pierreglaser .