remove duplicate atk GN config

The atk GN configs were moved to a separate GN file in
https://codereview.chromium.org/1909273002 but it appears
that the original configs were not removed, and are still
referenced.  Let's remove the old configs and just use
the new ones.

And while we're at it, add an assertion to check that glib
is enabled when atk is.

BUG=632297

TBR=agrieve@chromium.org

Review-Url: https://codereview.chromium.org/2251673004
Cr-Original-Commit-Position: refs/heads/master@{#412680}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 902b5282bf5c0314c801fa29a27ae1e4d39a56bc

config/linux/atk/BUILD.gn

@@ -4,6 +4,7 @@
 
 import("//build/config/features.gni")
 import("//build/config/linux/pkg_config.gni")
+import("//build/config/ui.gni")
 
 # CrOS doesn't install GTK, gconf or any gnome packages.
 assert(!is_chromeos)
@@ -13,7 +14,11 @@ assert(!is_chromeos)
 # tools for a CrOS build.
 assert(current_toolchain == default_toolchain)
 
-pkg_config("atk") {
+if (use_atk) {
+  assert(use_glib, "use_atk=true requires that use_glib=true")
+}
+
+pkg_config("atk_base") {
   packages = [ "atk" ]
   atk_lib_dir = exec_script(pkg_config_script,
                             pkg_config_args + [
@@ -27,7 +32,9 @@ pkg_config("atk") {
 # gn orders flags on a target before flags from configs. The default config
 # adds -Wall, and these flags have to be after -Wall -- so they need to
 # come from a config and can't be on the target directly.
-config("warnings") {
+config("atk") {
+  configs = [ ":atk_base" ]
+
   cflags = [
     # glib uses the pre-c++11 typedef-as-static_assert hack.
     "-Wno-unused-local-typedef",