Remove Expect from core library.

tests/language/multi_pass_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.
 // Dart test for loading several dart files and resolving superclasses lazily.
 
 library MultiPassTest.dart;
+import "package:expect/expect.dart";
 part "multi_pass_a.dart";
 part "multi_pass_b.dart";
 
 
 class Base {
   Base(this.value) { }
   var value;
 }
 
 class MultiPassTest {
   static testMain() {
     var a = new B(5);
     Expect.equals(5, a.value);
   }
 }
 
 main() {
   MultiPassTest.testMain();
 }