pkg/scheduled_test: fix analyzer hints

test/scheduled_server_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.
 
 library scheduled_server_test;
 
 import 'dart:async';
-import 'dart:io';
 
 import 'package:http/http.dart' as http;
 import 'package:scheduled_test/scheduled_server.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 import 'package:shelf/shelf.dart' as shelf;
 
-import 'package:metatest/metatest.dart';
 import 'utils.dart';
 
 void main() {
   expectTestPasses("a server with no handlers does nothing", () {
     new ScheduledServer();
   });
 
   expectServerError("a server with no handlers that receives a request throws "
       "an error", () {
     var server = new ScheduledServer();
@@ skipping 150 matching lines @@
     // (because it's given an ad-hoc stack trace).
     expect(errors.length, inInclusiveRange(1, 3));
     expect(errors[0].error.toString(), errorMessage);
 
     for (var i = 1; i < errors.length; i++) {
       if (errors[i].error == errors[0].error) continue;
       expect(errors[i].error, new isInstanceOf<http.ClientException>());
     }
   });
 }