Remove sysupgrade
Sysupgrade is present in Turris OS 5.0+. We should remove it. It is a dangerous to have it in system.
Reported here and confirmed: https://forum.turris.cz/t/bricked-turris-omnia-after-turris-os-5-0-sysupgrade-openwrt-19-07-2/12558?u=pepe