refactor: remove unused import

- Removed unused import statement for SetEqualityHelper
- This change simplifies the code and removes an unnecessary dependency

Author: fulleni

lib/src/services/default_user_preference_limit_service.dart

@@ -1,6 +1,5 @@
 import 'package:core/core.dart';
 import 'package:data_repository/data_repository.dart';
-import 'package:flutter_news_app_api_server_full_source_code/src/helpers/set_equality_helper.dart';
 import 'package:flutter_news_app_api_server_full_source_code/src/services/user_preference_limit_service.dart';
 import 'package:logging/logging.dart';