When removing a `config interface` section in `/etc/config/network`, drop related `rule` and `rule6` sections too, as well as related `dhcp` sections in `/etc/config/dhcp`. Ref: https://forum.openwrt.org/t/grooming-etc-config/109764/7 Signed-off-by: Jo-Philipp Wich <jo@mein.io> (cherry picked from commit 63034c36073bedf87db18d05d3fe8cca016c6490)