Hide cancel buttons without JavaScript

Hide the cancel buttons in the reply and add new topic forms without
JavaScript. They don't make sense here, as in the JavaScript version
of the site they hide the forms. Turning these into anchors would be
a very confusing experience as these might take users to an unexpected
place.

Adding browser test support.

Change-Id: Iaa778dd517e7719b305dc0d44fb1661b12aabbe5
Merge "Hide cancel buttons without JavaScript" into frontend-rewrite