at-spi2-core: fix systemdLibs dependency (#433749)

pkgs/by-name/at/at-spi2-core/package.nix

···
   libXi,
   libXext,
   gnome,
-  systemd,
-  systemdSupport ? lib.meta.availableOn stdenv.hostPlatform systemd,
+  systemdLibs,
+  systemdSupport ? lib.meta.availableOn stdenv.hostPlatform systemdLibs,
 }:
 
 stdenv.mkDerivation rec {
···
   ]
   ++ lib.optionals systemdSupport [
     # libsystemd is a needed for dbus-broker support
-    systemd
+    systemdLibs
   ];
 
   # In atspi-2.pc dbus-1 glib-2.0