atomic-host: Drop writing /etc/sysconfig/firstboot

We don't include firstboot in AH, we use cloud-init, so nothing
is ever going to parse this.  Drop it, since it shows up as a delta
in `ostree admin config-diff`, and further we want to reduce the
amount of stuff in this ks.

Signed-off-by: Colin Walters <walters@verbum.org>

fedora-atomic.ks

@@ -104,9 +104,6 @@ EOF
 echo "Disabling tmpfs for /tmp."
 systemctl mask tmp.mount
 
-# make sure firstboot doesn't start
-echo "RUN_FIRSTBOOT=NO" > /etc/sysconfig/firstboot
-
 # Uncomment this if you want to use cloud init but suppress the creation
 # of an "ec2-user" account. This will, in the absence of further config,
 # cause the ssh key from a metadata source to be put in the root account.