Remove __name__ == '__main__' check from modules

[eric-wieser]

These modules do not make sense to run from the command line, so should not have these lines.

At any rate, these lines do nothing.

[codecov]

Codecov Report

Merging #69 into master will decrease coverage by 0.06%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #69      +/-   ##
==========================================
- Coverage    66.7%   66.63%   -0.07%     
==========================================
  Files           8        8              
  Lines        4890     4880      -10     
==========================================
- Hits         3262     3252      -10     
  Misses       1628     1628

Impacted Files	Coverage Δ
galgebra/printer.py	77.29% <ø> (-0.05%)	⬇️
galgebra/lt.py	42.8% <ø> (-0.2%)	⬇️
galgebra/mv.py	61.65% <ø> (-0.05%)	⬇️
galgebra/ga.py	74.68% <ø> (-0.05%)	⬇️
galgebra/metric.py	70.93% <ø> (-0.14%)	⬇️

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