pkg/scheduled_test: fix analyzer hints

test/scheduled_test/unhandled_error_test.dart

 // Copyright (c) 2014, 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 'package:metatest/metatest.dart';
 import '../utils.dart';
 
 void main() {
   expectTestFails("a top-leveled error should be converted to a schedule error",
       () {
     schedule(() {
       new Future.microtask(() => throw 'error');
       return pumpEventQueue();
     });
   }, (errors) {
     expect(errors.first.error, equals('error'));
   });
 }