The target-x86_64.conf sysconfig file has been empty and essentially ignored
now for several years. This change removes the unused file to enable moving
towards a stateless configuration.

Signed-off-by: Ikey Doherty <michael.i.doherty@intel.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>