simplified code across the app and consolidated duplicated helpers

lib/api/marianumcloud/talk/get_shared_items/get_shared_items.dart

@@ -1,5 +1,3 @@
-import 'package:http/http.dart' as http;
-
 import '../../nextcloud_ocs.dart';
 import '../talk_api.dart';
 import 'get_shared_items_response.dart';
@@ -30,11 +28,4 @@ class GetSharedItems extends TalkApi<GetSharedItemsResponse> {
   @override
   GetSharedItemsResponse assemble(String raw) =>
       GetSharedItemsResponse.fromOcs(NextcloudOcs.decode(raw));
-
-  @override
-  Future<http.Response> request(
-    Uri uri,
-    Object? body,
-    Map<String, String>? headers,
-  ) => http.get(uri, headers: headers);
 }

lib/api/marianumcloud/talk/get_shared_items/get_shared_items_overview.dart

@@ -1,5 +1,3 @@
-import 'package:http/http.dart' as http;
-
 import '../../nextcloud_ocs.dart';
 import '../talk_api.dart';
 import 'get_shared_items_overview_response.dart';
@@ -18,11 +16,4 @@ class GetSharedItemsOverview extends TalkApi<GetSharedItemsOverviewResponse> {
   @override
   GetSharedItemsOverviewResponse assemble(String raw) =>
       GetSharedItemsOverviewResponse.fromOcs(NextcloudOcs.decode(raw));
-
-  @override
-  Future<http.Response> request(
-    Uri uri,
-    Object? body,
-    Map<String, String>? headers,
-  ) => http.get(uri, headers: headers);
 }