[[CHORE]] Revert parser improvements
[[CHORE]] Revert parser improvements

JSHint's validation for assignment within conditional clauses is derived
from code first contributed by GitHub user "usrbincc." That user could
not be reached to sign JSHint's Contributor License Agreement. Revert
the user's contribution to the application logic (preserving the
corresponding MIT-licensed test code) so that it may be re-written under
the terms of the Contributor License Agreement.

Revert the changes introduced by
b3d054e0188575892f29d2b13a524970c60fd8ea

thomas658/jshint,thomas658/jshint,jshint/jshint,jshint/jshint