pkg/scheduled_test: fix analyzer hints

test/scheduled_test/out_of_band_task_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 'package:scheduled_test/scheduled_test.dart';
 
-import 'package:metatest/metatest.dart';
 import '../utils.dart';
 
 void main() {
   setUpMockClock();
 
   expectTestPasses("out-of-band schedule() runs its function immediately (but "
       "asynchronously)", () {
     mockClock.run();
     schedule(() {
       expect(sleep(1).then((_) {
@@ skipping 14 matching lines @@
     var scheduleRun = false;
     expect(sleep(1).then((_) {
       schedule(() => sleep(1).then((_) {
         scheduleRun = true;
       }));
     }), completes);
 
     currentSchedule.onComplete.schedule(() => expect(scheduleRun, isTrue));
   });
 }