Remove Expect from core library.

tests/language/var_init_test.dart

 // Copyright (c) 2011, 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.
 // Testing correct initialization of variables in scopes.
 
+import "package:expect/expect.dart";
+
 class VarInitTest {
   static void testMain() {
     for (int i = 0; i < 10; i++) {
       var x;
       Expect.equals(null, x);
       x = 1;
     }
   }
 }
 
 main() {
   VarInitTest.testMain();
 }