networking: Remove empty directory

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
apt: Add new 99bcfg2 apt.conf.d file

Remove the old 50unattended-upgrades file and instead ship a single
99bcfg2 file which contains all the apt settings including
unattended-upgrades.

At this point, two things are supported, unattended-uprades origin
configuration and http proxy configuration.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>