Fixes RN iOS (#4053)

Summary:
Pull Request resolved: https://github.com/facebook/flipper/pull/4053

Update usage of RN `RCTBundleURLProvider` `jsBundleURLForBundleRoot` API.

The previous signature was removed in the current used RN version.

Reference:
https://github.com/facebook/react-native/blob/main/React/Base/RCTBundleURLProvider.h

Reviewed By: aigoncharov

Differential Revision: D39256797

fbshipit-source-id: 2074698597f691f46f6ffd2f6b569e7742d5fffc

react-native/ReactNativeFlipperExample/ios/ReactNativeFlipperExample/AppDelegate.m

@@ -65,8 +65,7 @@ static void InitializeFlipper(UIApplication* application) {
 - (NSURL*)sourceURLForBridge:(RCTBridge*)bridge {
 #if DEBUG
   return
-      [[RCTBundleURLProvider sharedSettings] jsBundleURLForBundleRoot:@"index"
-                                                     fallbackResource:nil];
+      [[RCTBundleURLProvider sharedSettings] jsBundleURLForBundleRoot:@"index"];
 #else
   return [[NSBundle mainBundle] URLForResource:@"main"
                                  withExtension:@"jsbundle"];