Remove last use of setRef()

Summary: This is hacky but it's the last place using `setRef()` and we need to think up an alternative API for www to replace it. In the meantime I'd like to kill the `(set|append)Ref` functions on the various array classes.

Reviewed By: billf

Differential Revision: D14884601

fbshipit-source-id: 31ebd2358277fd97cac37c5dffe08c78d5f0c81d

hphp/runtime/vm/event-hook.cpp

@@ -301,7 +301,9 @@ static Variant call_intercept_handler(
     }
     intArgs = par.append(done).toArray();
   } else {
-    intArgs = par.appendRef(done).toArray();
+    Variant tmp;
+    tmp.assignRef(done);
+    intArgs = par.appendWithRef(tmp).toArray();
   }
 
   auto ret = Variant::attach(