remove empty :not selectors (simpler alternative to PR #446)

[fabianonunes]

Fixes #353
Fixes #370 (partially)

This is simpler alternative to PR #446. It only removes empty :not() selectors and doesn't try to fix dangling commas

After depseudify, a :not pseudo-class may become an empty :not(). Calling document.querySelector with an empty :not raises an exception and the entire selector is kept, because jsdom#findAll optimistically ignores all errors.

This PR adds a second pass to dePseudify: after removal of ignoredPseudos, a new walk is performed in search of empty :not selectors.

Current behavior:

• dePseudify[.control:not(:checked)] => .control:not()
  • In this scenario, document.querySelector('.control:not()') raises an exception and the selector is kept.

Pull proposal:

• dePseudify[.control:not(:checked)] => .control
  • No empty :not()