Remove GN GYP generator.

tools/gn/secondary/net/third_party/nss/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("ssl_config") {
   include_dirs = [
     "//net/third_party/nss/ssl",
   ]
 }
 
 # TODO(brettw) move this to net/third_party/nss/ssl once GYP backwards-compat
 # is no longer needed.
 component("ssl") {
-  external = true
   # Not named "ssl" so the lib doesn't conflict with OpenSSL's libssl
   output_name = "crssl"
 
   sources = [
     "ssl/authcert.c",
     "ssl/cmpcert.c",
     "ssl/derive.c",
     "ssl/dtlscon.c",
     #"ssl/os2_err.c",
     #"ssl/os2_err.h",
@@ skipping 60 matching lines @@
   }
 
   if (is_linux) {
     include_dirs = [ "bodge" ]
     configs += [ "//third_party/nss:nss_linux_config" ]
   }
   if (is_mac) {
     sources -= [ "ssl/bodge/secitem_array.c" ]
   }
 }