Remove unused enable_node_monitoring option

Back in 1a7f7245e7 we dropped the one
place this was used, but left all of the variable and definitions and
garbage around cluster/

cluster/rackspace/config-default.sh

@@ -38,9 +38,6 @@ MINION_NAMES=($(eval echo ${INSTANCE_PREFIX}-minion-{1..${NUM_MINIONS}}))
 KUBE_NETWORK="10.240.0.0/16"
 SERVICE_CLUSTER_IP_RANGE="10.0.0.0/16"  # formerly PORTAL_NET
 
-# Optional: Install node monitoring.
-ENABLE_NODE_MONITORING=true
-
 # Optional: Enable node logging.
 ENABLE_NODE_LOGGING=false
 LOGGING_DESTINATION=elasticsearch

cluster/rackspace/util.sh

@@ -203,7 +203,6 @@ rax-boot-minions() {
         -e "s|DNS_SERVER_IP|${DNS_SERVER_IP:-}|" \
         -e "s|DNS_DOMAIN|${DNS_DOMAIN:-}|" \
         -e "s|ENABLE_CLUSTER_DNS|${ENABLE_CLUSTER_DNS:-false}|" \
-        -e "s|ENABLE_NODE_MONITORING|${ENABLE_NODE_MONITORING:-false}|" \
         -e "s|ENABLE_NODE_LOGGING|${ENABLE_NODE_LOGGING:-false}|" \
         -e "s|INDEX|$((i + 1))|g" \
         -e "s|KUBELET_TOKEN|${KUBELET_TOKEN}|" \