remove composite_key duplication in nrpe_lookup table

[lucabello]

Bug Description

Once vector is started when relating to nrpe (either after #59 is resolved or by additionally deploying filebeat), the file /etc/vector/nrpe_lookup.csv contains duplicate lines for composite keys.

If you juju ssh cos-proxy/0 you would see that

ubuntu@juju-142d1e-0:~$ cat /etc/vector/nrpe_lookup.csv
composite_key,juju_application,juju_unit,command,ipaddr
10.211.43.179_check_conntrack,ubuntu,ubuntu/0,check_conntrack,10.211.43.179
10.211.43.179_check_systemd_scopes,ubuntu,ubuntu/0,check_systemd_scopes,10.211.43.179
10.211.43.179_check_reboot,ubuntu,ubuntu/0,check_reboot,10.211.43.179
10.211.43.179_check_conntrack,ubuntu,ubuntu/0,check_conntrack,10.211.43.179
10.211.43.179_check_systemd_scopes,ubuntu,ubuntu/0,check_systemd_scopes,10.211.43.179
10.211.43.179_check_reboot,ubuntu,ubuntu/0,check_reboot,10.211.43.179

This duplication causes the log format to be weird and to not be correctly parsed from Grafana when using the Loki datasource.
The code responsible for this duplication should be here.

To Reproduce

machine model

1. juju deploy ubuntu
2. juju deploy nrpe
3. juju deploy cos-proxy
4. juju relate nrpe ubuntu
5. juju relate cos-proxy nrpe

k8s model

1. juju deploy cos-lite --channel=edge
2. cross-model relate cos-proxy to loki

Environment

∮ microk8s version
MicroK8s v1.26.1 revision 4596
∮ juju --version
3.1.0-genericlinux-amd64
∮ lxd --version
5.12

Relevant log output

-

Additional context

No response