Only new vertical format login and signup forms

* The "VForm" templates replace existing templates.
* Remove useNew switch logic and $wgUseVForm{UserLogin,CreateAccount}.
* The CSS and JS files for forms lose the .vform qualifier, except for
  the CSS for styling vform elements.
* Merge tiny mediawiki.special.userLogin.signup.js into createAccount.js.
* Remove replaced and obsolete messages (see
  https://www.mediawiki.org/wiki/Account_creation_user_experience/Strings
  for details), and remove mention of "new" forms and useNew from
  MessagesQqq.php.

Bug: 46333
Change-Id: I50f25583c3aa9a4a263fb40f50256f92c18ddb4d
Merge "Only new vertical format login and signup forms"