deleteOldTranslations method
Deletes old translations from the local database.
The duration parameter is the duration of the old translations.
Implementation
@override
Future<int> deleteOldTranslations(Duration duration) {
final DateTime thresholdDate = DateTime.now().subtract(duration);
return (delete(translations)..where((t) => t.createdAt.isSmallerThanValue(thresholdDate))).go();
}