Remove GN GYP generator.

tools/gn/secondary/testing/gtest/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("gtest_config") {
   defines = [
     "UNIT_TEST",
 
     # In order to allow regex matches in gtest to be shared between Windows
     # and other systems, we tell gtest to always use it's internal engine.
@@ skipping 15 matching lines @@
       # compiler will be 4.3.2. or newer.  The Mac, for example, uses
       # 4.2.1 as that is the latest available on that platform.  gtest
       # must be instructed that RTTI is disabled here, and for any
       # direct dependents that might include gtest headers.
       "GTEST_HAS_RTTI=0",
     ]
   }
 }
 
 static_library("gtest") {
-  external = true
-  gyp_file = "gtest.gyp"
   sources = [
     "include/gtest/gtest-death-test.h",
     "include/gtest/gtest-message.h",
     "include/gtest/gtest-param-test.h",
     "include/gtest/gtest-printers.h",
     "include/gtest/gtest-spi.h",
     "include/gtest/gtest-test-part.h",
     "include/gtest/gtest-typed-test.h",
     "include/gtest/gtest.h",
     "include/gtest/gtest_pred_impl.h",
@@ skipping 29 matching lines @@
     ]
   }
 
   include_dirs = [ "." ]
 
   all_dependent_configs = [ ":gtest_config" ]
 
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ "//build/config/compiler:no_chromium_code" ]
 }