migrated holidays module to MarianumConnect API, replaced local Holiday model.

lib/state/app/basis/dataloader/holiday_data_loader.dart

@@ -1,8 +0,0 @@
-import 'package:dio/dio.dart';
-
-import '../../infrastructure/data_loader/data_loader.dart';
-
-abstract class HolidayDataLoader<TResult> extends DataLoader<TResult> {
-  HolidayDataLoader()
-    : super(Dio(BaseOptions(baseUrl: 'https://ferien-api.de/api/v1/')));
-}