pkg/scheduled_test: fix analyzer hints

test/scheduled_test/nested_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("nested schedule() runs its function immediately (but "
       "asynchronously)", () {
     schedule(() {
       var nestedScheduleRun = false;
       schedule(() {
@@ skipping 49 matching lines @@
       "expect(..., completes) should report exceptions once", () {
     schedule(() {
       expect(schedule(() {
         throw 'error';
       }), completes);
 
       return pumpEventQueue();
     });
   }, (error) => expect(error, equals('error')));
 }