Remove unused imports in pub.

sdk/lib/_internal/pub/test/serve/utils.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS d.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.
 
 library pub_tests;
 
 import 'dart:async';
-import 'dart:io';
 
 import 'package:http/http.dart' as http;
 import 'package:scheduled_test/scheduled_process.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 
-import '../descriptor.dart' as d;
 import '../test_pub.dart';
 
 /// The pub process running "pub serve".
 ScheduledProcess _pubServer;
 
 /// The ephemeral port assigned to the running server.
 int _port;
 
 /// Schedules starting the "pub serve" process.
 ///
@@ skipping 38 matching lines @@
 
 /// Schedules an HTTP request to the running pub server with [urlPath] and
 /// verifies that it responds with a 404.
 void requestShould404(String urlPath) {
   schedule(() {
     return http.get("http://localhost:$_port/$urlPath").then((response) {
       expect(response.statusCode, equals(404));
     });
   }, "request $urlPath");
 }