Form control collections should not hold removed controls.

wkrev.com/20260 introduced a Firefox-compatible behavior which did not remove
form controls from a form control collection if a control is accessed by its
name. This behavior doesn't conform to the HTML standard and isn't compatible
with recent IE. We remove this behavior.

BUG=190026

Review URL: https://chromiumcodereview.appspot.com/23088009

git-svn-id: svn://svn.chromium.org/blink/trunk@156140 bbb929c8-8fbe-4397-9dbb-9b2b20218538