Revert "Dart2js support for custom element lifecycle events"

tests/html/utils.dart

Index: tests/html/utils.dart
diff --git a/tests/html/utils.dart b/tests/html/utils.dart
index 04c8235353f0303d9a0ce03b5971b9d6f0414c15..2533f24997b2a34e3694967f82611187efaafa29 100644
--- a/tests/html/utils.dart
+++ b/tests/html/utils.dart
@@ -159,17 +159,3 @@ void validateNodeTree(Node a, Node b, [String path = '']) {
     validateNodeTree(a.nodes[i], b.nodes[i], '$path[$i].');
   }
 }
-
-Future loadCustomElementPolyfill() {
-  if (!document.supportsRegister) {
-    var script = new ScriptElement()
-        ..src = '/packages/custom_element/custom-elements.debug.js';
-    document.head.append(script);
-    return document.body.on['WebComponentsReady'].first;
-  }
-  return new Future.value();
-}
-
-Future loadPolyfills() {
-  return loadCustomElementPolyfill();
-}