pkg: analysis aided cleanup

pkg/watcher/test/no_subscription_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 'dart:async';
-import 'dart:io';
 
 import 'package:scheduled_test/scheduled_test.dart';
 import 'package:watcher/watcher.dart';
 
 import 'utils.dart';
 
 main() {
   initConfig();
 
   setUp(createSandbox);
@@ skipping 47 matching lines @@
     writeFile("added.txt");
 
     // Wait until we get an event for the third file.
     schedule(() => completer.future);
 
     schedule(() {
       subscription.cancel();
     });
   });
 }