mediawiki.util: Remove test for jsMessage

mediawiki.util: Remove test for jsMessage

jsMessage uses mw.notify, which involves an animation.

mw.notify yields an mw.Notification object which has a reference
to the relevant elements.

However the deprecated jsMessage wrapper only returns boolean, so
we have no link to the element and no way to wait for the
animation to finish.

We could set up a mock clock in the test to skip the animation.
However, in this case the test was already useless as method
isn't testable (hardcoded booolean return).

This test was causing the QUnit test suite to fail occasionally
as the mw.notify animation was unfinished and would leak into
other tests.

Change-Id: Iffa91a3969bf69264b585e27ca44f85883ae2892