pkg/scheduled_test: fix analyzer hints

test/descriptor/file_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: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('file().create() creates a file', () {
     scheduleSandbox();
 
     d.file('name.txt', 'contents').create();
 
     schedule(() {
       expect(new File(path.join(sandbox, 'name.txt')).readAsString(),
@@ skipping 161 matching lines @@
           .writeAsString('barfoobaz');
     });
 
     d.binaryMatcherFile('name.txt', contains(12)).validate();
   }, (error) {
     expect(error.toString(), equals(
         "Expected: contains <12>\n"
         "  Actual: [98, 97, 114, 102, 111, 111, 98, 97, 122]\n"));
   });
 }