Remove dead code related to compositing from Sky

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

Index: sky/engine/core/rendering/style/StyleRareNonInheritedData.h
diff --git a/sky/engine/core/rendering/style/StyleRareNonInheritedData.h b/sky/engine/core/rendering/style/StyleRareNonInheritedData.h
index c6eae11f546814c274fee2247cea8141bb7febc2..703a59f71a84b5abcf3afbb58d41380d10b74f75 100644
--- a/sky/engine/core/rendering/style/StyleRareNonInheritedData.h
+++ b/sky/engine/core/rendering/style/StyleRareNonInheritedData.h
@@ -152,12 +152,6 @@ public:
     // 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&);