Remove unused line from file_system_watcher_test.

tests/standalone/io/file_system_watcher_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:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
 
@@ skipping 82 matching lines @@
 
   asyncStart();
   var sub;
   sub = watcher.listen((event) {
     if (event is FileSystemDeleteEvent) {
       Expect.isTrue(event.path.endsWith('file'));
       sub.cancel();
       asyncEnd();
       dir.deleteSync(recursive: true);
     }
-  }, onDone: () {
-    Expect.isTrue(gotEvent);
   }, onError: (e) {
     dir.deleteSync(recursive: true);
     throw e;
   });
 
   file.deleteSync();
 }
 
 
 void testWatchOnlyModifyFile() {
@@ skipping 126 matching lines @@
 
 void main() {
   testWatchCreateFile();
   testWatchModifyFile();
   testWatchMoveFile();
   testWatchDeleteFile();
   testWatchOnlyModifyFile();
   testMultipleEvents();
   testWatchNonRecursive();
 }