head-node: Do not attempt to restart ‘tor’ on unattended upgrades.

This is a followup to 8eb35e4f.

* head-node.scm <unattended-upgrade-configuration>[services-to-restart]:
Remove ‘tor’.

head-node.scm

@@ -481,7 +481,7 @@ CALENDAR, a gexp, and ensures at least FREE-SPACE GiB are available."
                           (unattended-upgrade-configuration
                            (operating-system-file this-file)
                            (services-to-restart
-                            '(mcron nginx guix-daemon qemu-binfmt tor unattended-upgrade))
+                            '(mcron nginx guix-daemon qemu-binfmt unattended-upgrade))
                            (channels
                             #~(cons* (channel
                                       (name 'cuirass)