Special:AllMessages: Remove al_title and allmessages-customised classes

Special:AllMessages: Remove al_title and allmessages-customised classes

* The al_title class was unused, and thus removed.

* The allmessages-customised class was used in CSS to target
  elements with 'al_default' and 'al_actual' classses within it,
  which are in turn only used for that purpose.
  Change the HTML to match the needs of the CSS by only setting
  al_default/al_actual classes on customised messages and remove
  need for the parent element class.

On a plain install this reduced output by ~2K from 75.8K to 74.0K,
and allocate 100 (2x50) fewer attribute nodes.

Change-Id: If2dd4cf5c937935f03f30b8410a32b6821b0bf34