udev: Enable delegation without delegating any controllers

Delegation is enabled for udev so that it can mess around with the
cgroup hierarchy to avoid killing control processes when it calls
cg_kill in on_post() when it goes idle. We don't actually care about
any specific cgroup controllers in udev, so set Delegate= to enable
delegation without delegating any controllers

Follow up for systemd#22752

Author: DaanDeMeyer

units/systemd-udevd.service.in

@@ -26,7 +26,7 @@ Conflicts=soft-reboot.target
 
 [Service]
 CapabilityBoundingSet=~CAP_SYS_TIME CAP_WAKE_ALARM
-Delegate=pids
+Delegate=
 DelegateSubgroup=udev
 Type=notify-reload
 # Note that udev will reset the value internally for its workers