Revert "Integrate NBI and Prometheus"

This reverts commit 38f5d583.

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

Change-Id: I90dbb6e1c2921289ecaabfa636878763f981c3e1
Signed-off-by: Mark Beierl <mark.beierl@canonical.com>