Remove Expect from core library.

tests/corelib/date_time5_test.dart

 // Copyright (c) 2012, 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:expect/expect.dart";
+
 // Test DateTime constructor with optional arguments.
 
 main() {
   var d = new DateTime(2012);
   Expect.equals(2012, d.year);
   Expect.equals(1, d.month);
   Expect.equals(1, d.day);
   Expect.equals(0, d.hour);
   Expect.equals(0, d.minute);
   Expect.equals(0, d.second);
@@ skipping 55 matching lines @@
 
   d = new DateTime(2012, 5, 15, 13, 21, 33, 12);
   Expect.equals(2012, d.year);
   Expect.equals(5, d.month);
   Expect.equals(15, d.day);
   Expect.equals(13, d.hour);
   Expect.equals(21, d.minute);
   Expect.equals(33, d.second);
   Expect.equals(12, d.millisecond);
 }