[prefect] fix caddy config

hosts/prefect/services/caddy.nix

···
       # Authentication
       ${pns.pocket-id.extUrl} = {
         extraConfig = ''
-          reverse_proxy / ${marvin}:${toString pns.pocket-id.port} {
-            header_up X-Real-IP {remote_host}
-            header_up X-Http-Version {http.request.proto}
-          }
+          reverse_proxy ${marvin}:${toString pns.pocket-id.port}
         '';
       };