r/vmhost: Disable DynamicUsers for vm-autostart

_libvirt_ has gone full Polkit, which doesn't work with systemd dynamic
users.  So, we have to run `vm-autostart` as root (with no special
OS-level privileges) in order for Polkit to authorize the connection to
the daemon socket.

roles/vmhost/files/vm-autostart.service

@@ -12,8 +12,6 @@ Environment=LIBVIRT_DEFAULT_URI=qemu:///system
 ExecStart=/usr/local/libexec/vm-autostart.sh
 Restart=on-failure
 
-DynamicUser=yes
-SupplementaryGroups=libvirt
 CapabilityBoundingSet=
 DeviceAllow=
 DevicePolicy=closed