Removed all analyzer issues from tests

runtime/observatory/tests/service/dev_fs_test.dart

 // Copyright (c) 2016, 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.
 // VMOptions=--error_on_bad_type --error_on_bad_override
 
-import 'dart:async';
 import 'dart:convert';
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
 
 var tests = [
   (VM vm) async {
     var result = await vm.invokeRpcNoUpgrade('_listDevFS', {});
     expect(result['type'], equals('FSList'));
     expect(result['fsNames'].toString(), equals("[]"));
@@ skipping 129 matching lines @@
 
     // Delete DevFS.
     result = await vm.invokeRpcNoUpgrade('_deleteDevFS', {
         'fsName': fsId,
     });
     expect(result['type'], equals('Success'));
   },
 ];
 
 main(args) async => runVMTests(args, tests);