chore: remove watcher polling option (#7480)

* remove watcher polling

* fix lint

* add db migration

mobile/openapi/test/system_config_library_watch_dto_test.dart

@@ -21,16 +21,6 @@ void main() {
       // TODO
     });
 
-    // int interval
-    test('to test the property `interval`', () async {
-      // TODO
-    });
-
-    // bool usePolling
-    test('to test the property `usePolling`', () async {
-      // TODO
-    });
-
 
   });