Fix jump-to-nav element overlap on RCFilters

Fix jump-to-nav element overlap on RCFilters

"Jump to: navigation, search" (English version of message) is visible on
Vector and Monobook when user tabs through the page.

Hiding #contentSub element in Ifcde40c66fbb caused margin to be removed
between title and "jump-to" element. Similar changes to #contentSub were
made in Id58972b4b7ca, but reverted in I84c890511113, because it caused
T178626. English Wikipedia acted with changing MediaWiki:Common.css file
(last two selectors in the file, at the time of writing this). That
customization makes this bug not appearing on enwiki.

Bug: T181154
Change-Id: I421cebec2acfd3ffe0cebd325f0fe2214dc5a8d7