Remove Expect from core library.

tests/standalone/io/secure_builtin_roots_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";
 import "dart:isolate";
 
 void testGoogleUrl() {
   ReceivePort keepAlive = new ReceivePort();
   HttpClient client = new HttpClient();
 
   void testUrl(String url) {
     var requestUri = Uri.parse(url);
@@ skipping 20 matching lines @@
 }
 
 void InitializeSSL() {
   SecureSocket.initialize();
 }
 
 void main() {
   InitializeSSL();
   testGoogleUrl();
 }