Remove Flatcar Linux Edge os_image option

* Flatcar Linux has not published an Edge channel image since
April 2020 and recently removed mention of the channel from
their documentation flatcar/Flatcar#345
* Users of Flatcar Linux Edge should move to the stable, beta, or
alpha channel, barring any alternate advice from upstream Flatcar
Linux

flatcar-linux/kubernetes/cl/controller.yaml

@@ -64,7 +64,6 @@ systemd:
         Wants=rpc-statd.service
         [Service]
         Environment=KUBELET_IMAGE=quay.io/poseidon/kubelet:v1.20.4
-        Environment=KUBELET_CGROUP_DRIVER=${cgroup_driver}
         ExecStartPre=/bin/mkdir -p /etc/kubernetes/cni/net.d
         ExecStartPre=/bin/mkdir -p /etc/kubernetes/manifests
         ExecStartPre=/bin/mkdir -p /opt/cni/bin
@@ -93,7 +92,6 @@ systemd:
           --authentication-token-webhook \
           --authorization-mode=Webhook \
           --bootstrap-kubeconfig=/etc/kubernetes/kubeconfig \
-          --cgroup-driver=$${KUBELET_CGROUP_DRIVER} \
           --client-ca-file=/etc/kubernetes/ca.crt \
           --cluster_dns=${cluster_dns_service_ip} \
           --cluster_domain=${cluster_domain_suffix} \

flatcar-linux/kubernetes/cl/worker.yaml

@@ -36,7 +36,6 @@ systemd:
         Wants=rpc-statd.service
         [Service]
         Environment=KUBELET_IMAGE=quay.io/poseidon/kubelet:v1.20.4
-        Environment=KUBELET_CGROUP_DRIVER=${cgroup_driver}
         ExecStartPre=/bin/mkdir -p /etc/kubernetes/cni/net.d
         ExecStartPre=/bin/mkdir -p /etc/kubernetes/manifests
         ExecStartPre=/bin/mkdir -p /opt/cni/bin
@@ -68,7 +67,6 @@ systemd:
           --authentication-token-webhook \
           --authorization-mode=Webhook \
           --bootstrap-kubeconfig=/etc/kubernetes/kubeconfig \
-          --cgroup-driver=$${KUBELET_CGROUP_DRIVER} \
           --client-ca-file=/etc/kubernetes/ca.crt \
           --cluster_dns=${cluster_dns_service_ip} \
           --cluster_domain=${cluster_domain_suffix} \

flatcar-linux/kubernetes/profiles.tf

@@ -106,7 +106,6 @@ data "template_file" "controller-configs" {
     domain_name            = var.controllers.*.domain[count.index]
     etcd_name              = var.controllers.*.name[count.index]
     etcd_initial_cluster   = join(",", formatlist("%s=https://%s:2380", var.controllers.*.name, var.controllers.*.domain))
-    cgroup_driver          = var.os_channel == "flatcar-edge" ? "systemd" : "cgroupfs"
     cluster_dns_service_ip = module.bootstrap.cluster_dns_service_ip
     cluster_domain_suffix  = var.cluster_domain_suffix
     ssh_authorized_key     = var.ssh_authorized_key
@@ -134,7 +133,6 @@ data "template_file" "worker-configs" {
 
   vars = {
     domain_name            = var.workers.*.domain[count.index]
-    cgroup_driver          = var.os_channel == "flatcar-edge" ? "systemd" : "cgroupfs"
     cluster_dns_service_ip = module.bootstrap.cluster_dns_service_ip
     cluster_domain_suffix  = var.cluster_domain_suffix
     ssh_authorized_key     = var.ssh_authorized_key

flatcar-linux/kubernetes/variables.tf

@@ -12,11 +12,11 @@ variable "matchbox_http_endpoint" {
 
 variable "os_channel" {
   type        = string
-  description = "Channel for a Flatcar Linux (flatcar-stable, flatcar-beta, flatcar-alpha, flatcar-edge)"
+  description = "Channel for a Flatcar Linux (flatcar-stable, flatcar-beta, flatcar-alpha)"
 
   validation {
-    condition     = contains(["flatcar-stable", "flatcar-beta", "flatcar-alpha", "flatcar-edge"], var.os_channel)
-    error_message = "The os_channel must be flatcar-stable, flatcar-beta, flatcar-alpha, or flatcar-edge."
+    condition     = contains(["flatcar-stable", "flatcar-beta", "flatcar-alpha"], var.os_channel)
+    error_message = "The os_channel must be flatcar-stable, flatcar-beta, or flatcar-alpha."
   }
 }