Remove dead code related to compositing from Sky

sky/engine/core/rendering/style/StyleRareNonInheritedData.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 134 matching lines @@
     unsigned m_justifyItemsOverflowAlignment : 2; // OverflowAlignment
     unsigned m_justifyItemsPositionType: 1; // Whether or not alignment uses the 'legacy' keyword.
 
     unsigned m_justifySelf : 4; // ItemPosition
     unsigned m_justifySelfOverflowAlignment : 2; // OverflowAlignment
 
     // ScrollBehavior. 'scroll-behavior' has 2 accepted values, but ScrollBehavior has a third
     // value (that can only be specified using CSSOM scroll APIs) so 2 bits are needed.
     unsigned m_scrollBehavior: 2;
 
-    // Plugins require accelerated compositing for reasons external to blink.
-    // In which case, we need to update the RenderStyle on the RenderEmbeddedObject,
-    // so store this bit so that the style actually changes when the plugin
-    // becomes composited.
-    unsigned m_requiresAcceleratedCompositingForExternalReasons: 1;
-
 private:
     StyleRareNonInheritedData();
     StyleRareNonInheritedData(const StyleRareNonInheritedData&);
 };
 
 } // namespace blink
 
 #endif  // SKY_ENGINE_CORE_RENDERING_STYLE_STYLERARENONINHERITEDDATA_H_