Remove optional variable networking on Digital Ocean

* Calico isn't viable on Digital Ocean because their firewalls
do not support IP-IP protocol. Its not viable to run a cluster
without firewalls just to use Calico.
* Remove the caveat note. Don't allow users to shoot themselves
in the foot

digital-ocean/container-linux/kubernetes/README.md

@@ -12,7 +12,7 @@ Typhoon distributes upstream Kubernetes, architectural conventions, and cluster
 ## Features <a href="https://www.cncf.io/certification/software-conformance/"><img align="right" src="https://storage.googleapis.com/poseidon/certified-kubernetes.png"></a>
 
 * Kubernetes v1.9.6 (upstream, via [kubernetes-incubator/bootkube](https://github.com/kubernetes-incubator/bootkube))
-* Single or multi-master, workloads isolated on workers, [Calico](https://www.projectcalico.org/) or [flannel](https://github.com/coreos/flannel) networking
+* Single or multi-master, workloads isolated on workers, [flannel](https://github.com/coreos/flannel) networking
 * On-cluster etcd with TLS, [RBAC](https://kubernetes.io/docs/admin/authorization/rbac/)-enabled, [network policy](https://kubernetes.io/docs/concepts/services-networking/network-policies/)
 * Ready for Ingress, Prometheus, Grafana, and other optional [addons](https://typhoon.psdn.io/addons/overview/)
 

digital-ocean/container-linux/kubernetes/bootkube.tf

@@ -6,7 +6,7 @@ module "bootkube" {
   api_servers           = ["${format("%s.%s", var.cluster_name, var.dns_zone)}"]
   etcd_servers          = "${digitalocean_record.etcds.*.fqdn}"
   asset_dir             = "${var.asset_dir}"
-  networking            = "${var.networking}"
+  networking            = "flannel"
   network_mtu           = 1440
   pod_cidr              = "${var.pod_cidr}"
   service_cidr          = "${var.service_cidr}"

digital-ocean/container-linux/kubernetes/variables.tf

@@ -71,12 +71,6 @@ variable "asset_dir" {
   type        = "string"
 }
 
-variable "networking" {
-  description = "Choice of networking provider (flannel or calico)"
-  type        = "string"
-  default     = "flannel"
-}
-
 variable "pod_cidr" {
   description = "CIDR IPv4 range to assign Kubernetes pods"
   type        = "string"