pkg/http_server: removed unused imports

pkg/http_server/test/virtual_directory_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 'dart:async';
 import 'dart:io';
 
 import "package:http_server/http_server.dart";
-import "package:path/path.dart";
 import "package:unittest/unittest.dart";
 
 import 'utils.dart';
 
 
 void main() {
   group('serve-root', () {
     test('dir-exists', () {
       expect(HttpServer.bind('localhost', 0).then((server) {
         var dir = Directory.systemTemp.createTempSync('http_server_virtual_');
@@ skipping 667 matching lines @@
         return getAsString(server.port, '/')
             .whenComplete(() {
               server.close();
               dir.deleteSync(recursive: true);
             });
       }), completion(equals('file contents')));
     });
   });
 }