nixos/pretix: fix state directory mode

The state directory contains static files that need to be accessible by
a webserver, but homeMode defaults to 0750 and switching the generation
will always force the homeMode, thereby breaking access to the assets.

Instead, fully rely on systemd to provide the StateDirectory with the
correct mode.

nixos/modules/services/web-apps/pretix.nix

@@ -569,11 +569,9 @@ in
     };
 
     users = {
-      groups."${cfg.group}" = {};
-      users."${cfg.user}" = {
+      groups.${cfg.group} = {};
+      users.${cfg.user} = {
         isSystemUser = true;
-        createHome = true;
-        home = cfg.settings.pretix.datadir;
         inherit (cfg) group;
       };
     };