Remove usage of dart:utf from dart:io.

tests/standalone/io/http_auth_digest_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.
 
 import "package:crypto/crypto.dart";
 import "package:expect/expect.dart";
 import 'dart:async';
 import 'dart:io';
 import 'dart:isolate';
-import 'dart:utf';
 
 class Server {
   HttpServer server;
   int unauthCount = 0;  // Counter of the 401 responses.
   int successCount = 0;  // Counter of the successful responses.
   int nonceCount = 0;  // Counter of use of current nonce.
   var ha1;
 
   static Future<Server> start(String algorithm,
                               String qop,
@@ skipping 369 matching lines @@
   testAuthenticateCallback(null, null);
   testAuthenticateCallback("MD5", null);
   testAuthenticateCallback("MD5", "auth");
   testAuthenticateCallback("MD5", "auth-int");
   testStaleNonce();
   testNextNonce();
   // These teste are not normally run. They can be used for locally
   // testing with another web server (e.g. Apache).
   //testLocalServerDigest();
 }