To answer my own question:
1. Comment out wifi-live-or-reset in /etc/rc.local
2. Go to /etc/modules.d, move away all kernel modules for the wireless interface, e.g.:
chdir /etc/modules.d
mkdir .NOT
mv 26-ath 27-ath9k-common 28-ath9k 50-wdt-ath79 .NOT
Reboot, and there will be no wireless interface.
No idea whether this is the easiest way to achieve this goal, but looking through all the init scripts, i couldn't figure out an esker way. Especailly this "wifi-live-or-reset" is a real nasty piece of system config, especially when you do not know about it, and for example try to disable the wifi interface in the expanded config web interface - and get periodic reboots after 2 minutes or so.