gn: Stop asserting on |use_gconf| when looking for atk.

build/config/linux/atk/BUILD.gn

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/features.gni")
 import("//build/config/linux/pkg_config.gni")
 
 # CrOS doesn't install GTK, gconf or any gnome packages.
-assert(!is_chromeos && use_gconf)
+assert(!is_chromeos)
 
 # These packages should _only_ be expected when building for a target.
 # If these extra checks are not run, gconf is required when building host
 # tools for a CrOS build.
 assert(current_toolchain == default_toolchain)
 
 pkg_config("atk") {
   packages = [ "atk" ]
   atk_lib_dir = exec_script(pkg_config_script,
                             pkg_config_args + [
@@ skipping 11 matching lines @@
   cflags = [
     # glib uses the pre-c++11 typedef-as-static_assert hack.
     "-Wno-unused-local-typedef",
 
     # G_DEFINE_TYPE automatically generates a *get_instance_private
     # inline function after glib 2.37. That's unused. Prevent to
     # complain about it.
     "-Wno-unused-function",
   ]
 }