fix analyzer warnings in stocks app

sky/examples/stocks2/lib/stock_settings.dart

 // Copyright 2015 The Chromium Authors. 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:sky' as sky;
-
 import 'package:sky/theme2/colors.dart' as colors;
 import 'package:sky/theme2/typography.dart' as typography;
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/checkbox.dart';
 import 'package:sky/widgets/icon_button.dart';
-import 'package:sky/widgets/menu_divider.dart';
 import 'package:sky/widgets/menu_item.dart';
 import 'package:sky/widgets/navigator.dart';
-import 'package:sky/widgets/raised_button.dart';
 import 'package:sky/widgets/scaffold.dart';
 import 'package:sky/widgets/tool_bar.dart';
 
 class StockSettings extends Component {
 
   StockSettings(this._navigator);
 
   Navigator _navigator;
 
   bool _awesome = false;
@@ skipping 31 matching lines @@
     );
   }
 
   Widget build() {
     return new Scaffold(
       toolbar: buildToolBar(),
       body: buildSettingsPane()
     );
   }
 }