Don't restart container-startup-done

nixos/modules/virtualisation/container-config.nix

@@ -99,6 +99,7 @@ with lib;
           '';
         serviceConfig.Type = "oneshot";
         serviceConfig.RemainAfterExit = true;
+        restartIfChanged = false;
       };
 
   };

nixos/modules/virtualisation/containers.nix

@@ -225,6 +225,7 @@ in
             # writes something to this pipe.  FIXME: it also hangs
             # until the start timeout expires if systemd-nspawn exits.
             read x < $root/var/lib/startup-done
+            rm -f $root/var/lib/startup-done
           '';
 
         preStop =