QA: remove moderation_anon test

The moderation_anon test no longer serves a purpose, since
deleted topics are not visible to anyone.

Also, this test executes an explicit logout, which interferes with
other tests using Selenium_user. Browser tests should never logout.
Any test requiring logout should use the API to create the
appropriate conditions before launching a browser session as
an anonymous user.

Change-Id: I7394ca8fc4133267cf6bb39163415f3f6b6165be