gnome: Drop unused directory

This cannot have been used in Nixpkgs, as it would imply IFD.

External users should have either pinned a version, or not used this as
a public API. Sorry.

gnome/default.nix

@@ -1,43 +0,0 @@
-{ pkgs }:
-
-rec {
-
-  mkBackgroundProperties = { backgroundName, backgroundFile }:
-    pkgs.substituteAll {
-      name = "${backgroundName}.xml";
-
-      src = ./share/gnome-background-properties/template.xml.in;
-
-      inherit backgroundName backgroundFile;
-    };
-    
-  mkBackgroundOverride = { name, background }:
-    pkgs.writeTextFile {
-      inherit name;
-      destination = "/share/gsettings-schemas/${name}/org.gnome.desktop.background.nixos.gschema.override";
-      text = ''
-        [org.gnome.desktop.background]
-        picture-uri='file://${background}'
-      '';
-    };
-
-  mkBackground = { backgroundName, backgroundFile }: rec {
-    properties = mkBackgroundProperties {
-      inherit backgroundName backgroundFile;
-    };
-
-    gsettings = mkBackgroundOverride {
-      name = "nixos-${backgroundName}-background";
-      background = properties;
-    };
-  };
-
-  # Compatibility with previous attribute.
-  gnomeDark = nix-wallpaper-simple-dark-gray-bottom;
-
-  nix-wallpaper-simple-dark-gray-bottom = mkBackground {
-    backgroundName = "nixos-dark";
-    backgroundFile = ../wallpapers/nix-wallpaper-simple-dark-gray_bottom.png;
-  };
-
-}

gnome/share/gnome-background-properties/template.xml.in

@@ -1,12 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<!DOCTYPE wallpapers SYSTEM "gnome-wp-list.dtd">
-<wallpapers>
-  <wallpaper deleted="false">
-    <name>@backgroundName@</name>
-    <filename>@backgroundFile@</filename>
-    <options>zoom</options>
-    <shade_type>solid</shade_type>
-    <pcolor>#ffffff</pcolor>
-    <scolor>#000000</scolor>
-  </wallpaper>
-</wallpapers>