smartd: no selftests scheduled

The default configuration of smartd already works, but does not run any self tests, however only the tests are said to have a chance to successfully warn before an imminent drive failure or data-loss.

The smartd configuration is trivial (https://ownyourbits.com/2018/11/10/monitor-your-hard-drive-health-with-smart-daemon/), it even supports drop-in scripts in /etc/smartmontools/run.d, unfortunately freedombox is complicating things too much for me to just chip in a script.

Ideally the short test would only be run once a day whenever the drive was woken up (has spin-up) anyway.