In the past, we emitted `unicast_peer` block even with empty unicast peers list.
This now results in:
```
Keepalived_vrrp[392762]: A unicast keyword has been specified without any unicast peers. Defaulting to multicast. This usage is deprecated - please update your configuration.
```
We do not emit it anymore to avoid this warning.
Tracking scripts in particular, cannot be included in extraOpts, because script declaration has to be above script usage in keepalived.conf.
Changes are fully backward compatible.