Revert "Fixing CharacterData.remove not working on FireFox."

tests/html/cdata_test.dart

-// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file
-
-library cdata_test;
-import '../../pkg/unittest/lib/unittest.dart';
-import '../../pkg/unittest/lib/html_config.dart';
-import 'dart:html';
-
-
-main() {
-  test('remove', () {
-    var div = new Element.html('<div>content</div>');
-    var cdata = div.nodes[0];
-    expect(cdata is CharacterData, true);
-    expect(cdata, isNotNull);
-    expect(div.innerHtml, 'content');
-
-    cdata.remove();
-    expect(div.innerHtml, '');
-  });
-}