Remove Expect from core library.

tests/corelib/list_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.
 
+import "package:expect/expect.dart";
+
 class ListTest {
 
   static testMain() {
     testList();
     testExpandableList();
   }
 
   static void expectValues(list, val1, val2, val3, val4) {
     Expect.equals(true, list.length == 4);
     Expect.equals(true, list.length == 4);
@@ skipping 128 matching lines @@
   }
 }
 
 class Yes {
   operator ==(var other) => true;
 }
 
 main() {
   ListTest.testMain();
 }