Remove uses of PaintBehaviorFlattenCompositingLayers

sky/engine/core/rendering/PaintPhase.h

Index: sky/engine/core/rendering/PaintPhase.h
diff --git a/sky/engine/core/rendering/PaintPhase.h b/sky/engine/core/rendering/PaintPhase.h
index c4570dc0fa04e15a8ad8de5d916aa9e98bc81ab9..59bc803a67a0ecf558f4b7c953c8cf597438ea1c 100644
--- a/sky/engine/core/rendering/PaintPhase.h
+++ b/sky/engine/core/rendering/PaintPhase.h
@@ -55,10 +55,8 @@ enum PaintBehaviorFlags {
     PaintBehaviorNormal = 0,
     // FIXME(sky): Renumber these once we're done deleting them.
     PaintBehaviorForceBlackText = 1 << 1,
-    // FIXME(sky): This is unused. Remove it.
-    PaintBehaviorFlattenCompositingLayers = 1 << 2,
-    PaintBehaviorSkipRootBackground = 1 << 4,
-    PaintBehaviorRootBackgroundOnly = 1 << 5
+    PaintBehaviorSkipRootBackground = 1 << 2,
+    PaintBehaviorRootBackgroundOnly = 1 << 3
 };
 
 typedef unsigned PaintBehavior;