refactor(content_management): remove unused search change events

- Remove EditSourceCountrySearchChanged and EditSourceLanguageSearchChanged events
- These events were not being used in the bloc logic, likely because the UI already has direct access to the search text controllers

Author: fulleni

lib/content_management/bloc/edit_source/edit_source_event.dart

@@ -87,27 +87,11 @@ final class EditSourceSubmitted extends EditSourceEvent {
   const EditSourceSubmitted();
 }
 
-/// Event for when the country search term is changed.
-final class EditSourceCountrySearchChanged extends EditSourceEvent {
-  const EditSourceCountrySearchChanged(this.searchTerm);
-  final String searchTerm;
-  @override
-  List<Object?> get props => [searchTerm];
-}
-
 /// Event to request loading more countries.
 final class EditSourceLoadMoreCountriesRequested extends EditSourceEvent {
   const EditSourceLoadMoreCountriesRequested();
 }
 
-/// Event for when the language search term is changed.
-final class EditSourceLanguageSearchChanged extends EditSourceEvent {
-  const EditSourceLanguageSearchChanged(this.searchTerm);
-  final String searchTerm;
-  @override
-  List<Object?> get props => [searchTerm];
-}
-
 /// Event to request loading more languages.
 final class EditSourceLoadMoreLanguagesRequested extends EditSourceEvent {
   const EditSourceLoadMoreLanguagesRequested();