Cleanup some todos for gke + rip out dead AuthConfig code

cluster/kubectl.sh

@@ -105,15 +105,6 @@ if [[ "$KUBERNETES_PROVIDER" == "gke" ]]; then
   config=(
     "--context=gke_${PROJECT}_${ZONE}_${CLUSTER_NAME}"
   )
-  # In gcloud versions prior to 0.9.59, GKE stores its kubeconfig
-  # in a separate location. If the file doesn't exist, then use
-  # the default kubeconfig file.
-  # TODO(roberthbailey): Remove this once gcloud 0.9.59 or above is released.
-  if [[ -e "${HOME}/.config/gcloud/kubernetes/kubeconfig" ]]; then
-    config+=(
-      "--kubeconfig=${HOME}/.config/gcloud/kubernetes/kubeconfig"
-    )
-  fi
 elif [[ "$KUBERNETES_PROVIDER" == "ubuntu" ]]; then
   detect-master > /dev/null
   config=(