Remove Expect from core library.

tests/standalone/io/secure_server_closing_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.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 
+import "package:expect/expect.dart";
 import "dart:async";
 import "dart:io";
 import "dart:isolate";
 
 const SERVER_ADDRESS = "127.0.0.1";
 const HOST_NAME = "localhost";
 const CERTIFICATE = "localhost_cert";
 
 void testCloseOneEnd(String toClose) {
   ReceivePort port = new ReceivePort();
@@ skipping 138 matching lines @@
                           useBuiltinRoots: false);
 
   testCloseOneEnd("client");
   testCloseOneEnd("server");
   testCloseBothEnds();
   testPauseServerSocket();
   testCloseServer();
   // TODO(whesse): Add testPauseSocket from raw_socket_test.dart.
   // TODO(whesse): Add testCancelResubscribeSocket from raw_socket_test.dart.
 }