Remove enableStopSurfaceOnRootViewUnmount feature flag

Summary:
This feature flag (enableStopSurfaceOnRootViewUnmount) was used to gate usage of the "stopSurface" API, which is now fully supported, and has been used
in the FB app for several months. This is safe to ship in code.

Changelog: [Internal]

Reviewed By: mdvacca

Differential Revision: D25275192

fbshipit-source-id: fa22bfd00aa023297bc19c83c138f133e9ff1645

ReactAndroid/src/main/java/com/facebook/react/ReactRootView.java

@@ -41,7 +41,6 @@
 import com.facebook.react.bridge.WritableMap;
 import com.facebook.react.bridge.WritableNativeMap;
 import com.facebook.react.common.annotations.VisibleForTesting;
-import com.facebook.react.config.ReactFeatureFlags;
 import com.facebook.react.modules.appregistry.AppRegistry;
 import com.facebook.react.modules.core.DeviceEventManagerModule;
 import com.facebook.react.modules.deviceinfo.DeviceInfoModule;
@@ -489,7 +488,7 @@ public void unmountReactApplication() {
     // to be committed via the Scheduler, which will cause mounting instructions
     // to be queued up and synchronously executed to delete and remove
     // all the views in the hierarchy.
-    if (mReactInstanceManager != null && ReactFeatureFlags.enableStopSurfaceOnRootViewUnmount) {
+    if (mReactInstanceManager != null) {
       final ReactContext reactApplicationContext = mReactInstanceManager.getCurrentReactContext();
       if (reactApplicationContext != null && getUIManagerType() == FABRIC) {
         @Nullable

ReactAndroid/src/main/java/com/facebook/react/config/ReactFeatureFlags.java

@@ -74,9 +74,6 @@ public class ReactFeatureFlags {
   /** Feature flag to configure eager initialization of Fabric */
   public static boolean eagerInitializeFabric = false;
 
-  /** Feature flag to use stopSurface when ReactRootView is unmounted. */
-  public static boolean enableStopSurfaceOnRootViewUnmount = false;
-
   /** Use experimental SetState retry mechanism in view? */
   public static boolean enableExperimentalStateUpdateRetry = false;