Remove CSS regions support, keeping a bare minimum to support "region-based" multicol.

Source/core/rendering/RenderLayerStackingNode.cpp

Index: Source/core/rendering/RenderLayerStackingNode.cpp
diff --git a/Source/core/rendering/RenderLayerStackingNode.cpp b/Source/core/rendering/RenderLayerStackingNode.cpp
index eef589fe5097607e5314fc64a4f6c5b1a8a419dc..4d1b706f2cf04bbf4ae64d3ca0d89c1d00e812af 100644
--- a/Source/core/rendering/RenderLayerStackingNode.cpp
+++ b/Source/core/rendering/RenderLayerStackingNode.cpp
@@ -426,8 +426,7 @@ bool RenderLayerStackingNode::shouldBeNormalFlowOnlyIgnoringCompositedScrolling(
         || renderer()->hasClipPath()
         || renderer()->hasFilter()
         || renderer()->hasBlendMode()
-        || layer()->isTransparent()
-        || renderer()->style()->hasFlowFrom();
+        || layer()->isTransparent();
 
     return couldBeNormalFlow && !preventsElementFromBeingNormalFlow;
 }