nixos/xfce: don't set a bloated GST_PLUGIN_PATH

nixos/modules/services/x11/desktop-managers/xfce.nix

@@ -34,10 +34,6 @@ in
             # Set GTK_DATA_PREFIX so that GTK+ can find the Xfce themes.
             export GTK_DATA_PREFIX=${config.system.path}
 
-            # Necessary to get xfce4-mixer to find GST's ALSA plugin.
-            # Ugly.
-            export GST_PLUGIN_PATH=${config.system.path}/lib
-
             exec ${pkgs.stdenv.shell} ${pkgs.xfce.xinitrc}
           '';
       };