pkg/scheduled_test: removed unused imports

pkg/scheduled_test/test/scheduled_future_matchers_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 'package:scheduled_test/scheduled_test.dart';
 
 import 'metatest.dart';
 import 'utils.dart';
 
 void main(_, message) {
   initMetatest(message);
 
   setUpTimeout();
 
@@ skipping 60 matching lines @@
         throw 'error';
       }), completion(equals('bar')));
     });
 
     test('test 2', () {
       expect(errors, everyElement(new isInstanceOf<ScheduleError>()));
       expect(errors.map((e) => e.error), equals(['error']));
     });
   }, passing: ['test 2']);
 }