Remove Expect from core library.

tests/standalone/io/echo_server_stream_test.dart

 // Copyright (c) 2013, 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.
 //
 // Echo server test program to test socket streams.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 
 library ServerTest;
 
+import "package:expect/expect.dart";
 import "dart:io";
 import "dart:isolate";
 part "testing_server.dart";
 
 class EchoServerGame {
 
   static const MSGSIZE = 10;
   static const MESSAGES = 100;
   static const FIRSTCHAR = 65;
 
@@ skipping 106 matching lines @@
       Expect.fail("Socket error $e");
     }
 
     connection.listen(dataReceived, onError: errorHandler);
   }
 }
 
 main() {
   EchoServerGame echoServerGame = new EchoServerGame.start();
 }