Observatory: remove unused imports

runtime/observatory/tests/service/reload_sources_test.dart

 // Copyright (c) 2015, 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 'package:observatory/service_io.dart';
-import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
 import 'dart:developer';
 import 'service_test_common.dart';
 
 testMain() {
   debugger();  // Stop here.
   print('1');
   while (true) {
   }
 }
@@ skipping 17 matching lines @@
   resumeIsolate,
   // Verify that it is running.
   isolateIsRunning,
   // Reload sources and do not request to pause post reload.
   reloadSources(false),
   // Verify that it is running.
   isolateIsRunning,
 ];
 
 main(args) => runIsolateTests(args, tests, testeeConcurrent: testMain);