Updated grafana dashboard with dynamic rate_interval

- added in one place the rate_interval variable instead of static "[1m]".
- removed system_prometheus.json as its no longer in use

Related-Bug: PROD-30387

Change-Id: I7e1615409d3e767609e503d8e9f7d646d62ab08a
(cherry picked from commit 186a489777454f07ca5997b2c658009e2443ac1c)
2 files changed