Hide contentSub completely

Previously it was faded out to 60%. contentSub contains FlaggedRevs
stuff we don't want around in the editor, and contains the revision
navigation when editing an oldid, which James decided also shouldn't
be visible when editing.

Change-Id: Icdef98f756ce92a32d276d6eeb22c9de04640d8b
Merge "Hide contentSub completely"