MAINT: Remove LegacyGenerator

[bashtage]

Remove LegacyGenerator since it has been replaced by RandomState

[bashtage]

This pull request fixes 3 alerts when merging 11320c2 into 7779c6e - view on LGTM.com

fixed alerts:

• 3 for Explicit export is not defined

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Comment posted by LGTM.com

[codecov]

Codecov Report

Merging #62 into master will decrease coverage by <.01%.
The diff coverage is 96.66%.

@@            Coverage Diff             @@
##           master      #62      +/-   ##
==========================================
- Coverage   91.73%   91.72%   -0.01%     
==========================================
  Files          28       26       -2     
  Lines        7995     7701     -294     
  Branches      128      122       -6     
==========================================
- Hits         7334     7064     -270     
+ Misses        639      617      -22     
+ Partials       22       20       -2

Impacted Files	Coverage Δ
randomgen/entropy.pyx	87.5% <ø> (-0.18%)	⬇️
randomgen/pickle.py	84.21% <ø> (+1.23%)	⬆️
randomgen/legacy/__init__.py	0% <0%> (-100%)	⬇️
randomgen/generator.pyx	90.59% <100%> (+0.01%)	⬆️
randomgen/mtrand.pyx	90.41% <100%> (+0.01%)	⬆️
randomgen/pcg32.pyx	76.41% <100%> (-2.66%)	⬇️
randomgen/threefry32.pyx	79.52% <100%> (-2.3%)	⬇️
randomgen/dsfmt.pyx	78.94% <100%> (-1.95%)	⬇️
randomgen/pcg64.pyx	79.33% <100%> (-1.92%)	⬇️
randomgen/threefry.pyx	81.06% <100%> (-1.53%)	⬇️
... and 21 more

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