pkg/scheduled_test: fix analyzer hints

test/descriptor/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:path/path.dart' as path;
 import 'package:scheduled_test/descriptor.dart' as d;
 import 'package:scheduled_test/scheduled_test.dart';
 
-import 'package:metatest/metatest.dart';
 import 'utils.dart';
 
 void main() {
   expectTestPasses("directory().create() creates a directory and its contents",
       () {
     scheduleSandbox();
 
     d.dir('dir', [
       d.dir('subdir', [
         d.file('subfile1.txt', 'subcontents1'),
@@ skipping 358 matching lines @@
           "descriptor", path.join(sandbox, 'dir'));
       expect(descriptor, isDirectoryDescriptor('descriptor', [
         isDirectoryDescriptor('subdir', [
           isFileDescriptor('subfile1.txt', 'subcontents1')
         ]),
         isFileDescriptor('file1.txt', 'contents1')
       ]));
     });
   });
 }