gnome3.adwaita-icon-theme: remove empty dir tree

Also similar for old gnome2 icon theme.
/cc maintainer @lethalman.

pkgs/desktops/gnome-2/desktop/gnome-icon-theme/default.nix

···
 
   nativeBuildInputs = [ pkgconfig intltool iconnamingutils gtk ];
 
+  # remove a tree of dirs with no files within
+  postInstall = '' rm -r "$out/share/locale" '';
+
   meta = {
     platforms = stdenv.lib.platforms.linux;
   };

pkgs/desktops/gnome-3/3.16/core/adwaita-icon-theme/default.nix

···
   propagatedBuildInputs = [ hicolor_icon_theme ];
 
   buildInputs = [ gdk_pixbuf librsvg ];
-  
+
   nativeBuildInputs = [ pkgconfig intltool iconnamingutils gtk ];
+
+  # remove a tree of dirs with no files within
+  postInstall = '' rm -r "$out/locale" '';
 
   meta = with stdenv.lib; {
     platforms = platforms.linux;