Don't set `enabled: true` for systemd templates

Systemd units for systemd templates should not have enabled: true in it's ignition config spec.

This is because enabling a template as it is doesn't make sense:

sh-5.1# systemctl enable network-split-bc-setup@.timer
Failed to enable unit: Destination unit timers.target is a non-template unit.

Started to be a problem since OCP 4.13, when it prevents MCO to apply the configuration moving a machine into degraded state:

$ oc logs pod/machine-config-controller-7f488c778d-7zjvn -n openshift-machine-config-operator | tail -2
I0323 16:36:17.415050       1 node_controller.go:446] Pool worker: node compute-0: changed annotation machineconfiguration.openshift.io/state = Degraded
I0323 16:36:20.680758       1 status.go:108] Degraded Machine: compute-0 and Degraded Reason: error enabling units: Failed to enable unit: Destination unit timers.target is a non-template unit.