Remove Expect from core library.

tests/corelib/queue_single_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.
 
 library queue.single.test;
+import "package:expect/expect.dart";
 import 'dart:collection' show Queue;
 
 main() {
   Queue<int> queue1 = new Queue<int>();
   queue1.add(42);
   Queue queue2 = new Queue();
   queue2..add(11)
       ..add(12)
       ..add(13);
   Queue queue3 = new Queue();
 
   Expect.equals(42, queue1.single);
   Expect.throws(() => queue2.single, (e) => e is StateError);
   Expect.throws(() => queue3.single, (e) => e is StateError);
 }