Removed $wgImgAuthPublicTest

* For public wikis, using img_auth.php cannot hurt, and thumb.php
  is already available anyway. Treat it as always "false".

Change-Id: I1240e00386a76593c37c9ac7b4c1f547c655452d
Avoid bogus IE extension check errors in img_auth.php

Change-Id: I57083d3fe0517b94d3b786970b412e6ec51cf5f0
Merge "Removed $wgImgAuthPublicTest"
Merge "Avoid bogus IE extension check errors in img_auth.php"