Remove unused .fade class for admin message bars

[nacin]

In #11267 [12385], the pulse/fade effect was removed from admin message bars.

This class should be stripped from core. It's not just for the extraneous markup, but also so plugin developers know what markup is the best practice. (The class also appears inconsistently, apparently not used in some places where it should have been used. Any plugins styling or animating it are already not getting what they want.) If we ever wanted to add anything special back (or if a plugin wanted to), .updated should be animated directly.

[azaozz]

Fixed in [12546]