when upgrading from 1.3 to 1.4 we don’t clean up "grafana-dashboard-netobserv" , 2 NetObserv dashboard appear probably because the dashboard CM name changed to grafana-dashboard-netobserv-flow-metrics

IMO, we should clean up old dashboard.

Steps to reproduce:
1. Install 1.3 and flowcollector stack with 0-click loki
2. Edit subscription "oc edit subscription -n openshift-netobserv-operator" , edit spec.source to have 1.4 catalogsource
3.

$ oc get cm -A | egrep -i netobserv
...
openshift-config-managed                           grafana-dashboard-netobserv                                       1      5m29s
openshift-config-managed                           grafana-dashboard-netobserv-flow-metrics                          1      119s
openshift-config-managed                           grafana-dashboard-netobserv-health                                1      5m29s