remove serialization. it's moved to github

pkg/serialization/test/no_library_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.
-
-import 'package:serialization/serialization.dart';
-import 'package:unittest/unittest.dart';
-
-class Thing {
-  var name;
-}
-
-void main() {
-
-  test("Serializing something without a library directive", () {
-    var thing = new Thing()..name = 'testThing';
-    var s = new Serialization()
-      ..addRuleFor(Thing);
-    var serialized = s.write(thing);
-    var newThing = s.read(serialized);
-    expect(thing.name, newThing.name);
-  });
-}