"Your domain" appearance fixes for new forms

* Restore lost id=mw-user-domain-section (so wikitech can hide it).
* Remove obsolete pos-above class.
* Fix message key.

Bug: 49225
Change-Id: I73bcd44eff10a4fd2d1a392e82427e42e92fc3bf
Merge ""Your domain" appearance fixes for new forms"