Fix requestAnimationFrame in headless mode. Fixes #7296.

tests/wpt/mozilla/meta/mozilla/window_requestAnimationFrame2.html.ini

@@ -1,6 +0,0 @@
-[window_requestAnimationFrame2.html]
-  type: testharness
-  expected: TIMEOUT
-  [Test throwing an error inside requestAnimationFrame callback]
-    expected: NOTRUN
-

tests/wpt/mozilla/tests/mozilla/window_requestAnimationFrame.html

@@ -8,8 +8,6 @@
     <script>
     async_test(function() {
       window.requestAnimationFrame(this.step_func_done());
-      // FIXME(#7296)
-      setTimeout(this.step_func_done(), 500);
     });
     </script>
   </body>