Remove most of the old compositing code.

sky/engine/core/rendering/RenderBoxModelObject.h

Index: sky/engine/core/rendering/RenderBoxModelObject.h
diff --git a/sky/engine/core/rendering/RenderBoxModelObject.h b/sky/engine/core/rendering/RenderBoxModelObject.h
index 0e72fb8d53ad5b6a8b27e50d7a6f715e20d2e964..7ba49c5aa46b9351736d695b36104d422c194771 100644
--- a/sky/engine/core/rendering/RenderBoxModelObject.h
+++ b/sky/engine/core/rendering/RenderBoxModelObject.h
@@ -276,8 +276,6 @@ private:
     RoundedRect getBackgroundRoundedRect(const LayoutRect&, InlineFlowBox*, LayoutUnit inlineBoxWidth, LayoutUnit inlineBoxHeight,
         bool includeLogicalLeftEdge, bool includeLogicalRightEdge) const;
 
-    bool fixedBackgroundPaintsInLocalCoordinates() const;
-
     void clipBorderSidePolygon(GraphicsContext*, const RoundedRect& outerBorder, const RoundedRect& innerBorder,
                                BoxSide, bool firstEdgeMatches, bool secondEdgeMatches);
     void clipBorderSideForComplexInnerPath(GraphicsContext*, const RoundedRect&, const RoundedRect&, BoxSide, const class BorderEdge[]);