Fix uninstall using openshift_prometheus_state=absent

This was broken in https://github.com/openshift/openshift-ansible/pull/6811

bz: https://bugzilla.redhat.com/show_bug.cgi?id=1540806

playbooks/openshift-prometheus/private/uninstall.yml

@@ -5,4 +5,4 @@
   - name: Run the Prometheus Uninstall Role Tasks
     include_role:
       name: openshift_prometheus
-      tasks_from: uninstall
+      tasks_from: uninstall_prometheus