Remove Expect from core library.

tests/standalone/io/https_client_certificate_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";
 import "dart:async";
 import "dart:io";
 import "dart:uri";
 import "dart:isolate";
 
 const SERVER_ADDRESS = "127.0.0.1";
 const HOST_NAME = "localhost";
 
 int numClientCertificatesReceived = 0;
 
@@ skipping 73 matching lines @@
   var keepAlive = new ReceivePort();
   InitializeSSL();
   // Test two connections in sequence.
   test({'certificateName': null})()
       .then((_) => test({'certificateName': 'localhost_cert'})())
       .then((_) {
     Expect.equals(2, numClientCertificatesReceived);
     keepAlive.close();
   });
 }