Remove Expect from core library.

tests/standalone/io/socket_port_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:io";
 
 void testPort() {
   ServerSocket server = new ServerSocket("127.0.0.1", 0, 5);
 
   Socket clientSocket = new Socket("127.0.0.1", server.port);
 
   server.onConnection = (Socket socket) {
     Expect.equals(socket.port, server.port);
     Expect.equals(clientSocket.port, socket.remotePort);
     Expect.equals(clientSocket.remotePort, socket.port);
 
     server.close();
   };
 }
 
 void main() {
   testPort();
 }