Narrow draw merge branch orchestration

src/canvas.h

@@ -275,8 +275,7 @@ private:
         const Brush& brush,
         const glm::mat4& ortho,
         bool use_blend,
-        bool copy_blend_destination,
-        bool draw_checkerboard);
+        bool copy_blend_destination);
     void draw_merge_final_plane_composite(
         const glm::mat4& ortho,
         bool draw_checkerboard);