Remove outdated Grafana information (#8012)

substrate/.maintain/monitoring/grafana-dashboards/README_dashboard.md

@@ -5,10 +5,3 @@ Shared templated Grafana dashboards.
 To import the dashboards follow the [Grafana
 documentation](https://grafana.com/docs/grafana/latest/reference/export_import/).
 You can see an example setup [here](../../../.maintain/sentry-node).
-
-#### Required labels on Prometheus metrics
-
-- `instance` referring to a single scrape target (see [Prometheus docs for
-  details](https://prometheus.io/docs/concepts/jobs_instances/)).
-
-- `network` referring to the Blockchain network e.g. Kusama.