remove feature flag enableEarlyScheduledMountItemExecution (#41146)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/41146

changelog: [internal]

Remove old feature flag

Reviewed By: rshest

Differential Revision: D50537414

fbshipit-source-id: 93aa254ac285b8e03edfec1bec1238a220b9fdcf

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/config/ReactFeatureFlags.java

@@ -112,9 +112,6 @@ public class ReactFeatureFlags {
    */
   public static boolean enableRemoveDeleteTreeInstruction = false;
 
-  /** Temporary flag to allow execution of mount items up to 15ms earlier than normal. */
-  public static boolean enableEarlyScheduledMountItemExecution = false;
-
   /**
    * Allow closing the small gap that appears between paths when drawing a rounded View with a
    * border.

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/fabric/FabricUIManager.java

@@ -799,20 +799,6 @@ public class FabricUIManager implements UIManager, LifecycleEventListener {
           };
       if (UiThreadUtil.isOnUiThread()) {
         runnable.run();
-      } else {
-        // The Choreographer will dispatch any mount items,
-        // but it only gets called at the /beginning/ of the
-        // frame - it has no idea if, or when, there is actually work scheduled. That means if we
-        // have a big chunk of work
-        // scheduled but the scheduling happens 1ms after the
-        // start of a UI frame, we'll miss out on 15ms of time
-        // to perform the work (assuming a 16ms frame).
-        // The DispatchUIFrameCallback still has value because of
-        // the PreMountItems that we need to process at a lower
-        // priority.
-        if (ReactFeatureFlags.enableEarlyScheduledMountItemExecution) {
-          UiThreadUtil.runOnUiThread(runnable);
-        }
       }
     }