Remove Before=libvirt-guests.service from other services

libvirt-guests has After= dependency for all the sockets and that is enough.
With the extra Before= in the service file systemd postpones the start of the
socket activated service (when libvirt-guests is trying to connect to the
socket) until after libvirt-guests is stopped effectively making `systemctl stop
libvirt-guests` deadlock.  The reason for that is that all stop jobs are
scheduled before any start job.  Removing the redundant Before= specification
fixes this behaviour.

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>