pkg/unittest: fix imports

lib/html_enhanced_config.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.
 
 @deprecated
 library unittest.html_enhanced_config;
 
-import 'src/simple_configuration.dart';
+import 'src/deprecated/simple_configuration.dart';
 
 /// This is a stub class used to preserve compatibility with unittest 0.11.*.
 ///
 /// It will be removed before the next version is released.
 @deprecated
 class HtmlEnhancedConfiguration extends SimpleConfiguration {
   HtmlEnhancedConfiguration(bool isLayoutTest);
 
   void processMessage(e) {}
 }
 
 @deprecated
 void useHtmlEnhancedConfiguration([bool isLayoutTest]) {}