Remove unnecessary shell.error checks from common tests

[freitagbr]

Fixes #714

Removes the t.falsy(shell.error()) checks from methods that can't set the error state.

[codecov-io]

Codecov Report

Merging #785 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #785   +/-   ##
=======================================
  Coverage   95.39%   95.39%           
=======================================
  Files          33       33           
  Lines        1239     1239           
=======================================
  Hits         1182     1182           
  Misses         57       57

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[nfischer]

LGTM. Do any common methods set error (aside from common.error)?

[freitagbr]

The closure returned from wrap (i.e. any wrapped function) sets state.error to null, but those are covered in other tests obviously.