Remove prometheus operator from Kubespray (#2658)

Kubespray should not install any helm charts. This is a task
that a user should do on his/her own through ansible or another
tool. It opens the door to wrapping installation of any helm
chart.

roles/kubernetes-apps/meta/main.yml

@@ -27,12 +27,6 @@ dependencies:
       - apps
       - registry
 
-  - role: kubernetes-apps/metrics
-    when: prometheus_operator_enabled
-    tags:
-      - apps
-      - metrics
-
   # istio role should be last because it takes a long time to initialize and
   # will cause timeouts trying to start other addons.
   - role: kubernetes-apps/istio