Make index argument to HTMLOptionsCollection.remove() mandatory

Make index argument to HTMLOptionsCollection.remove() mandatory as per the
specification:
http://www.whatwg.org/specs/web-apps/current-work/multipage/common-dom-interfaces.html#htmloptionscollection-0

This behavior is consistent with Firefox 23 and IE10. It is confusing what
is expected to happen when no argument is given.

BUG=

Review URL: https://chromiumcodereview.appspot.com/23602016

git-svn-id: svn://svn.chromium.org/blink/trunk@157055 bbb929c8-8fbe-4397-9dbb-9b2b20218538