Use mw-ui-checkbox from core

mw-ui-checkbox is now a reusable mediawiki ui component without
a JavaScript dependency. This removes code from beta features that
is handled elsewhere (see I6a0db7c8ce33d242120f1cba9222db4e2154696c)

Update tests to reflect HTML changes.
Change-Id: I256a84f7c94ca04ce01ce62571e33ca2ec35c9f5
Merge "Use mw-ui-checkbox from core"