Delete mobile config react_fabric:finalize_updates_on_synchronous_upd…

…ate_view_ios

Summary:
changelog: [internal]

This was used as a kill switch, it has been in place for over 4 months, let's get rid of it.

Reviewed By: mdvacca

Differential Revision: D37921377

fbshipit-source-id: 594586033694766e13d0f2ab2bcd73b28ba180a9

React/Fabric/Mounting/RCTMountingManager.mm

@@ -324,10 +324,7 @@ - (void)synchronouslyUpdateViewOnUIThread:(ReactTag)reactTag
     componentView.layer.opacity = newViewProps.opacity;
   }
 
-  auto reactNativeConfig = _contextContainer->at<std::shared_ptr<ReactNativeConfig const>>("ReactNativeConfig");
-  if (reactNativeConfig && reactNativeConfig->getBool("react_fabric:finalize_updates_on_synchronous_update_view_ios")) {
-    [componentView finalizeUpdates:RNComponentViewUpdateMaskProps];
-  }
+  [componentView finalizeUpdates:RNComponentViewUpdateMaskProps];
 }
 
 - (void)synchronouslyDispatchCommandOnUIThread:(ReactTag)reactTag