chore(sb): use systemd kernel cmdline condition

pkgs/rootfs/secure-boot-enroll.sh

@@ -1,23 +1,9 @@
-#!/bin/bash
+#!/bin/sh
 set -ex -uo pipefail
 
-enroll=
-for o in $(< /proc/cmdline); do
-    case $o in
-        patos.secureboot=*)
-            enroll=${o#*=}
-            ;;
-    esac
-done
-
-if [ -z "$enroll" ]; then
-  echo 'No patos.secureboot= parameter on the kernel command line' >&2
-  exit 0
-fi
-
 SETUP_MODE=$(sbctl status --json | jq -r '.setup_mode')
 
-[ "$SETUP_MODE" = "false" -o "$enroll" != "true" ] && exit 0
+[ "$SETUP_MODE" = "false" ] && exit 0
 
 cat <<EOL> /run/sbctl.yml
 ---