You need to ask for removing your domain on this topic: Nohost domain recovery - Suppression de domaine en nohost.me, noho.st et ynh.fr - #1115 by Gofannon
And next, you can remove /etc/yunohost/dyndns and /etc/cron.d/yunohost-dyndns
Finally, run this commands:
yunohost dyndns subscribe -d domain
yunohost dyndns update