Remove Expect from core library.

tests/standalone/io/http_proxy_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";
 import "dart:uri";
 
 class Server {
   HttpServer server;
   int proxyHops;
   List<String> directRequestPaths;
   int requestCount = 0;
 
   Server(this.proxyHops, this.directRequestPaths) : server = new HttpServer();
@@ skipping 288 matching lines @@
 
 main() {
   testInvalidProxy();
   testDirectProxy();
   testProxy();
   testProxyChain();
   // This test is not normally run. It can be used for locally testing
   // with a real proxy server (e.g. Apache).
   // testRealProxy();
 }