Remove GN GYP generator.

tools/gn/secondary/skia/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.
 
 enable_printing = true  # TODO(brettw) pass this feature flag in somehow.
 skia_support_gpu = !is_ios
 skia_support_pdf = !is_ios && enable_printing
 
 # External-facing config for dependent code.
 config("skia_config") {
@@ skipping 1095 matching lines @@
 if (component_mode == "static_library") {
   group("skia") {
     deps = [
       ":skia_library",
       ":skia_chrome",
     ]
     forward_dependent_configs_from = deps
   }
 
   static_library("skia_library") {
-    external = true
     sources = skia_library_sources
 
     deps = [
       ":skia_opts",
       "//third_party/zlib",
     ]
 
     if (skia_support_pdf) {
       deps += [ "//third_party/sfntly" ]
     } else {
@@ skipping 17 matching lines @@
         "//third_party/icu:icuuc",
       ]
     }
   }
 
   config("skia_chrome_config") {
     include_dirs = [ "ext" ]
   }
 
   static_library("skia_chrome") {
-    external = true
     sources = skia_chrome_sources
 
     configs -= [ "//build/config/compiler:chromium_code" ]
     configs += [
       ":skia_config",
       "//build/config/compiler:no_chromium_code",
     ]
     direct_dependent_configs = [ ":skia_chrome_config" ]
 
     deps = [
@@ skipping 135 matching lines @@
     ":skia_config",
     "//build/config/compiler:no_chromium_code"
   ]
 
   if (is_linux) {
     cflags = [ "-msse3" ]
   } else if (is_mac) {
     cflags = [ "-mssse3" ] # Note the third 's'.
   }
 }