[Effen] remove the last traces of the 'display' property from the effen component library.

sky/tests/framework/basic.sky

 <import src="../resources/run-after-display.sky" />
 <script>
 import 'basic.dart';
 import 'dart:sky';
 import '../resources/dom_serializer.dart';
 import 'dart:sky.internals' as internals;
 
 void main() {
   new TestApp();
   runAfterDisplay(() {
-    var result = serializeNode(document.lastChild.previousSibling) + serializeNode(document.lastChild);
+    document.firstChild.remove();
+    document.firstChild.remove();
+    var result = serializeNode(document);
     try {
       internals.notifyTestComplete(result);
     } catch (e) {
       print(e);
       print(result);
     }
   });
 }
 </script>