Fix #23755 ("RCTImagePickerManager requires main queue setup" warning) (#24314)

Summary:
Fix #23755 - Which is to remove the warning:
```
Module RCTImagePickerManager requires main queue setup since it overrides `init` but doesn't implement `requiresMainQueueSetup`. In a future release React Native will default to initializing all native modules on a background thread unless explicitly opted-out of.
```

General Fixed - Warning "RCTImagePickerManager requires main queue setup
Pull Request resolved: https://github.com/facebook/react-native/pull/24314

Differential Revision: D14788772

Pulled By: cpojer

fbshipit-source-id: e2017136008367d36468debb258afa698b5402bc

Libraries/CameraRoll/RCTImagePickerManager.m

@@ -52,6 +52,11 @@ RCT_EXPORT_MODULE(ImagePickerIOS);
   return self;
 }
 
++ (BOOL)requiresMainQueueSetup
+{
+  return NO;
+}
+
 - (void)dealloc
 {
   [[NSNotificationCenter defaultCenter] removeObserver:self name:@"AVCaptureDeviceDidStartRunningNotification" object:nil];