Fabric: Optimizations in view flattening algorithm

Summary:
This diff changes the condition in `ViewShadowNode::isLayoutOnly()` removing checking for `onLayout` event listener.
We needed that before because the mechanism of emitting events was based on analyzing mutation instructures (we needed those to be generated for nodes with `onLayout`).
Recenly we changed that algorithm deeply integrating in layout infra, so we don't need this anymore.

Reviewed By: JoshuaGross, mdvacca

Differential Revision: D15273491

fbshipit-source-id: 2d43f00d1b87369d5993fe5ba70c2de36b8ce0c5

ReactCommon/fabric/components/view/ViewShadowNode.cpp

@@ -16,8 +16,6 @@ bool ViewShadowNode::isLayoutOnly() const {
   const auto &viewProps = *std::static_pointer_cast<const ViewProps>(props_);
 
   return viewProps.collapsable &&
-      // Event listeners
-      !viewProps.onLayout &&
       // Generic Props
       viewProps.nativeId.empty() &&
       // Accessibility Props