Delete remaining masks dead code.

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

Index: sky/engine/core/rendering/style/NinePieceImage.h
diff --git a/sky/engine/core/rendering/style/NinePieceImage.h b/sky/engine/core/rendering/style/NinePieceImage.h
index 303c48576a4723d5c5e6fc214d7d081c65e6b152..c9fded97d1ed8c1b05bd90af40f4d6cb6153bd51 100644
--- a/sky/engine/core/rendering/style/NinePieceImage.h
+++ b/sky/engine/core/rendering/style/NinePieceImage.h
@@ -110,13 +110,6 @@ public:
         m_data.access()->verticalRule = other.m_data->verticalRule;
     }
 
-    void setMaskDefaults()
-    {
-        m_data.access()->imageSlices = LengthBox(0);
-        m_data.access()->fill = true;
-        m_data.access()->borderSlices = BorderImageLengthBox(Length(Auto));
-    }
-
     static LayoutUnit computeOutset(const BorderImageLength& outsetSide, LayoutUnit borderSide)
     {
         if (outsetSide.isNumber())