Remove some unused code.

sdk/lib/_internal/pub/test/serve/watch_removed_file_test.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:io';
-
 import 'package:path/path.dart' as path;
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../../lib/src/io.dart';
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 import 'utils.dart';
 
 main() {
   initConfig();
   integration("stop serving a file that is removed", () {
     d.dir(appPath, [
       d.appPubspec(),
       d.dir("web", [
         d.file("index.html", "body")
       ])
     ]).create();
 
     startPubServe();
     requestShouldSucceed("index.html", "body");
 
     schedule(() => deleteEntry(
         path.join(sandboxDir, appPath, "web", "index.html")));
 
     waitForBuildSuccess();
     requestShould404("index.html");
     endPubServe();
   });
 }