Grafana: drop geard workers gauge
Grafana: drop geard workers gauge

This metric is no longer sent in newer versions of geard.  If we
aren't running it now, we will be soon.  Go ahead and drop it
from the graphs.

Change-Id: I2ee92f0673b28704a6e28b400554cd5a2c9642cd

openstack-infra/project-config,openstack-infra/project-config