network-manager-applet: Don't depend on webkitgtk by default

This added significant bloat to non-Gnome systems.

(cherry picked from commit 65b04b8bef07c710d6ec52b4f71854fabbbda2de)

pkgs/tools/networking/network-manager-applet/default.nix

···
 { stdenv, fetchurl, intltool, pkgconfig, libglade, networkmanager, gnome3
 , libnotify, libsecret, polkit, isocodes, modemmanager, librsvg
 , mobile_broadband_provider_info, glib_networking, gsettings_desktop_schemas
-, makeWrapper, udev, libgudev, hicolor_icon_theme, jansson, wrapGAppsHook, webkitgtk }:
+, makeWrapper, udev, libgudev, hicolor_icon_theme, jansson, wrapGAppsHook, webkitgtk
+, withGnome ? false }:
 
 stdenv.mkDerivation rec {
   name    = "${pname}-${major}.${minor}";
···
   buildInputs = [
     gnome3.gtk libglade networkmanager libnotify libsecret gsettings_desktop_schemas
     polkit isocodes makeWrapper udev libgudev gnome3.gconf gnome3.libgnome_keyring
-    modemmanager jansson librsvg glib_networking gnome3.dconf webkitgtk
-  ];
+    modemmanager jansson librsvg glib_networking gnome3.dconf
+  ] ++ stdenv.lib.optional withGnome webkitgtk;
 
   nativeBuildInputs = [ intltool pkgconfig wrapGAppsHook ];