Remove Expect from core library.

tests/standalone/io/http_advanced_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.
 //
 // 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';
 
 class TestServerMain {
   TestServerMain()
       : _statusPort = new ReceivePort(),
         _serverPort = null {
     _serverPort = spawnFunction(startTestServer);
   }
@@ skipping 455 matching lines @@
         return testCookies().then((_) {
           print('testFlush()');
           return testFlush();
         });
       });
     });
   }).then((_) {
     print('done');
   });
 }