Remove GN GYP generator.

tools/gn/secondary/testing/gmock/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.
 
 config("gmock_config") {
   # Gmock headers need to be able to find themselves.
   include_dirs = [ "include" ]
 }
 
 static_library("gmock") {
-  gyp_file = "gmock.gyp"
-  external = true
   sources = [
     # Sources based on files in r173 of gmock.
     "include/gmock/gmock-actions.h",
     "include/gmock/gmock-cardinalities.h",
     "include/gmock/gmock-generated-actions.h",
     "include/gmock/gmock-generated-function-mockers.h",
     "include/gmock/gmock-generated-matchers.h",
     "include/gmock/gmock-generated-nice-strict.h",
     "include/gmock/gmock-matchers.h",
     "include/gmock/gmock-spec-builders.h",
@@ skipping 13 matching lines @@
   # This project includes some stuff form gtest's guts.
   include_dirs = [ "../gtest/include" ]
 
   direct_dependent_configs = [
     ":gmock_config",
     "//testing/gtest:gtest_config",
   ]
 }
 
 static_library("gmock_main") {
-  external = true
-  gyp_file = "gmock.gyp"
   sources = [ "src/gmock_main.cc" ]
   deps = [ ":gmock" ]
 }