Remove disable_interface from dhcp-all-interfaces

I don't actually think there is a way that disable_interface
would get called on Fedora... because if config_exists
it takes a different path. Furthermore we really don't
want to mess w/ configured interfaces in dhcp-all-interfaces
because that could be side effecty (and is arguably the
job os os-net-config anyways).

This function already did nothing on Debian so removing
shouldn't hurt anything.

Change-Id: Ic53bbab98aa03d487efd290ae8e076045781b5b1
Merge "Remove disable_interface from dhcp-all-interfaces"