Remove Prometheus addon and it's tests

Prometheus addon was developed for exterimental and test purpose only.
As readme states it should not be used by anyone.

hack/ginkgo-e2e.sh

@@ -163,7 +163,6 @@ export PATH
   --node-tag="${NODE_TAG:-}" \
   --master-tag="${MASTER_TAG:-}" \
   --cluster-monitoring-mode="${KUBE_ENABLE_CLUSTER_MONITORING:-standalone}" \
-  --prometheus-monitoring="${KUBE_ENABLE_PROMETHEUS_MONITORING:-false}" \
   --dns-domain="${KUBE_DNS_DOMAIN:-cluster.local}" \
   --ginkgo.slowSpecThreshold="${GINKGO_SLOW_SPEC_THRESHOLD:-300}" \
   ${KUBE_CONTAINER_RUNTIME:+"--container-runtime=${KUBE_CONTAINER_RUNTIME}"} \