seatd: declare the runtime dir with systemd.tmpfiles instead of sane.fs

hosts/common/programs/seatd.nix

@@ -40,7 +40,7 @@ lib.mkMerge [
   (lib.mkIf cfg.enabled {
     users.groups.seat = {};
 
-    sane.fs."${seatdDir}".dir.acl = {
+    systemd.tmpfiles.settings."20-sane-seatd"."${seatdDir}".d = {
       user = "root";
       group = "seat";
       mode = "0770";
@@ -50,8 +50,6 @@ lib.mkMerge [
       description = "Seat management daemon";
       documentation = [ "man:seatd(1)" ];
 
-      after = [ config.sane.fs."${seatdDir}".unit ];
-      wants = [ config.sane.fs."${seatdDir}".unit ];
       wantedBy = [ "multi-user.target" ];
       restartIfChanged = false;