refactor(content_management): remove unused country loading event

- Remove CreateHeadlineLoadMoreCountriesRequested event
- This event was likely intended for loading more countries, but is no longer needed

Author: fulleni

lib/content_management/bloc/create_headline/create_headline_event.dart

@@ -83,9 +83,3 @@ final class CreateHeadlineStatusChanged extends CreateHeadlineEvent {
 final class CreateHeadlineSubmitted extends CreateHeadlineEvent {
   const CreateHeadlineSubmitted();
 }
-
-/// Event to request loading more countries.
-final class CreateHeadlineLoadMoreCountriesRequested
-    extends CreateHeadlineEvent {
-  const CreateHeadlineLoadMoreCountriesRequested();
-}