fixes #54017, remove deprecated --mode flag

cluster/gce/util.sh

@@ -1542,14 +1542,8 @@ function check-existing() {
   fi
 }
 
-# TODO(#54017): Remove below logics for handling deprecated network mode field.
-# `x_gcloud_mode` was replaced by `x_gcloud_subnet_mode` in gcloud 175.0.0 and
-# the content changed as well. Keeping such logic to make the transition eaiser.
 function check-network-mode() {
   local mode="$(gcloud compute networks list --filter="name=('${NETWORK}')" --project ${NETWORK_PROJECT} --format='value(x_gcloud_subnet_mode)' || true)"
-  if [[ -z "${mode}" ]]; then
-    mode="$(gcloud compute networks list --filter="name=('${NETWORK}')" --project ${NETWORK_PROJECT} --format='value(x_gcloud_mode)' || true)"
-  fi
   # The deprecated field uses lower case. Convert to upper case for consistency.
   echo "$(echo $mode | tr [a-z] [A-Z])"
 }