Remove GN GYP generator.

base/test/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/ui.gni")
 
 static_library("test_support_base") {
-  external = true
   sources = [
     "expectations/expectation.cc",
     "expectations/expectation.h",
     "expectations/parser.cc",
     "expectations/parser.h",
     "gtest_xml_util.cc",
     "gtest_xml_util.h",
     "launcher/test_launcher.cc",
     "launcher/test_launcher.h",
     "launcher/test_result.cc",
@@ skipping 99 matching lines @@
   if (toolkit_uses_gtk) {
     configs += [ "//build/config/linux:gtk" ]
   }
 }
 
 config("perf_test_config") {
   defines = [ "PERF_TEST" ]
 }
 
 static_library("test_support_perf") {
-  external = true
   sources = [
     "run_all_perftests.cc",
   ]
   deps = [
     "//base",
     "//testing/gtest",
   ]
 
   direct_dependent_configs = [ ":perf_test_config" ]
 
   if (toolkit_uses_gtk) {
     configs += [ "//build/config/linux:gtk" ]
   }
 }
 
 static_library("run_all_unittests") {
-  external = true
   sources = [
     "run_all_unittests.cc",
   ]
   deps = [
     ":test_support_base",
   ]
 }