Remove the custom certmon timer (polling via sha1sum every 60s),
replaced by the deployer's tls-cert-reload.path unit (inotify).
chatmail-init.sh: inject TLS_EXTERNAL_CERT_AND_KEY env var into
chatmail.ini at startup if not already present.
docker-compose.yaml: remove CMDEPLOY_STAGES, CHATMAIL_NOSYSCTL,
TLS_EXTERNAL_CERT_AND_KEY from base environment (set in init script
or via override file).