Fix applicationDidEnterBackground not being called (#48376)

Summary:
I noticed that `AppDelegate` subscribers listening for `applicationDidEnterBackground` events in Expo projects (as documented [here](https://github.com/expo/expo/blob/238b6f57e459dd2c0b13ee158f0af709fe922460/docs/pages/modules/appdelegate-subscribers.mdx?plain=1#L56) aren't working as expected anymore.
While investigating, I discovered that the events aren't reaching the `ExpoAppDelegate` implementation ([source](https://github.com/expo/expo/blob/71f2c55ff3f11e43ab43761bb5cece2e48eae0bf/packages/expo-modules-core/ios/AppDelegates/ExpoAppDelegate.swift#L61)) because the `RCTAppDelegate` implementation of `applicationDidEnterBackground` interrupts the event chain. This appears to be affecting some legitimate use cases.
I believe we could improve this by removing the current implementation, but I'd love to hear your thoughts on this approach. I might be missing some context about why this implementation was originally needed, so any insights would be greatly appreciated!

## Changelog:

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[IOS] [FIXED] - Fix applicationDidEnterBackground not being called

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[IOS] [FIXED] - Fix applicationDidEnterBackground not being called

Pull Request resolved: https://github.com/facebook/react-native/pull/48376

Test Plan: Ran a local test after change

Reviewed By: javache

Differential Revision: D67621557

Pulled By: cipolleschi

fbshipit-source-id: 2d73711372deba867bd616c79ef4d00c79aa86d5

packages/react-native/Libraries/AppDelegate/RCTAppDelegate.mm

@@ -84,11 +84,6 @@ using namespace facebook::react;
   [_window makeKeyAndVisible];
 }
 
-- (void)applicationDidEnterBackground:(UIApplication *)application
-{
-  // Noop
-}
-
 - (NSURL *)sourceURLForBridge:(RCTBridge *)bridge
 {
   [NSException raise:@"RCTBridgeDelegate::sourceURLForBridge not implemented"