Remove unneeded DHCP config option to vmdebootstrap

Created by: SunilMohanAdapa

With the option set, vmdebootstrap will generate an /etc/network/interfaces with DHCP configuration for eth0. Earlier this file was getting overwritten so no harm done. But now, we have a patch proposed to freedombox-setup that uses network-manager and will suffer if eth0 is mentioned in /etc/network/interfaces.