Revert "Integrate grafana-k8s and prometheus-k8s"

This reverts commit d8b46730.

Reason for revert: Grafana-k8s requires Juju 3.1 and we are not ready
to change Juju versions at this time

Change-Id: Ieb3d7d3713a180ab5cc45cd01cec31d4110512a0
Signed-off-by: Mark Beierl <mark.beierl@canonical.com>