nixos/atd: remove "batch" from setuid wrappers
"batch" is a shell script so invoking it via setuid wrapper never worked
anyway. (The kernel drops perms on executables with shebang.) A previous
nixpkgs commit made "batch" invoke the NixOS setuid "at" wrapper to gain
needed privileges.
Thanks to @yesbox for noticing.
(cherry picked from commit 497108b4568d01cefee6acdf92b738ee80e22023)
