Get rid of the use_glib gn variable.

build/config/linux/BUILD.gn

 # Copyright (c) 2013 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/linux/pkg_config.gni")
 import("//build/config/features.gni")
 import("//build/config/sysroot.gni")
 import("//build/config/ui.gni")
 import("//tools/generate_library_loader/generate_library_loader.gni")
 
@@ skipping 44 matching lines @@
 }
 
 config("fontconfig") {
   libs = [ "fontconfig" ]
 }
 
 pkg_config("freetype2") {
   packages = [ "freetype2" ]
 }
 
-pkg_config("glib") {
-  packages = [
-    "glib-2.0",
-    "gmodule-2.0",
-    "gobject-2.0",
-    "gthread-2.0",
-  ]
-}
-
 pkg_config("pangocairo") {
   packages = [ "pangocairo" ]
 }
 
 pkg_config("pangoft2") {
   packages = [ "pangoft2" ]
 }
 
 # Note: if your target also depends on //dbus, you don't need to add this
 # config (it will get added automatically if you depend on //dbus).
@@ skipping 159 matching lines @@
 
   functions = gypi_values.libudev_functions
 }
 
 group("udev") {
   deps = [
     ":udev0_loader",
     ":udev1_loader",
   ]
 }