Remove old sponsoring links

fixes https://bugs.cacert.org/view.php?id=1423

includes/sponsorinfo.php

@@ -1,8 +1,6 @@
   <div class="sponsorinfo">
     <?=_("CAcert operations are sponsored by")?>
     <a href="http://www.bit.nl/" target="_blank"><img class="sponsorlogo" src="/images/bit.png" alt="[BIT logo]" border="0"></a>
-    <a href="http://www.tunix.nl/" target="_blank"><img class="sponsorlogo" src="/images/tunix.png" alt="[TUNIX logo]" border="0"></a>
     <a href="http://www.nlnet.nl/" target="_blank"><img class="sponsorlogo" src="/images/nlnet.png" alt="[NLnet logo]" border="0"></a>
-    <a href="http://www.openarchitecturenetwork.org/" target="_blank"><img class="sponsorlogo" src="/images/oan.png" alt="[OAN logo]" border="0"></a>
   </div>