switch to an extension that is actually used

just 'cause it is in the `facebook/extensions/` dir doesn't mean we use it. I checked this one and it is loaded internally and not open source.
sosorry

hphp/test/slow/ext_hash/ext_hash.php

@@ -3,7 +3,7 @@
 // HPHP has has many version of these functions over time
 // Faceobok has impelemtnation differences
 function is_facebook() {
-  return extension_loaded("tao");
+  return extension_loaded("phpmcc");
 }
 
 function brown_fox() {