Remove GN GYP generator.

tools/gn/secondary/third_party/icu/BUILD.gn

 # Copyright (c) 2012 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.
 
 # Shared config used by ICU and all dependents.
 config("icu_config") {
   defines = [
     "U_USING_ICU_NAMESPACE=0",
   ]
   include_dirs = [
@@ skipping 27 matching lines @@
     cflags = [
       "-Wno-deprecated-declarations",
       "-Wno-logical-op-parentheses",
       "-Wno-tautological-compare",
       "-Wno-switch",
     ]
   }
 }
 
 component("icui18n") {
-  external = true
   sources = [
     "source/i18n/anytrans.cpp",
     "source/i18n/astro.cpp",
     "source/i18n/basictz.cpp",
     "source/i18n/bms.cpp",
     "source/i18n/bmsearch.cpp",
     "source/i18n/bocsu.c",
     "source/i18n/brktrans.cpp",
     "source/i18n/buddhcal.cpp",
     "source/i18n/calendar.cpp",
@@ skipping 152 matching lines @@
   configs += [
     "//build/config/compiler:rtti",
     "//build/config/compiler:no_chromium_code",
   ]
 
   configs += [ ":icu_code" ]
   direct_dependent_configs = [ ":icu_config" ]
 }
 
 component("icuuc") {
-  external = true
   sources = [
     "source/common/bmpset.cpp",
     "source/common/brkeng.cpp",
     "source/common/brkiter.cpp",
     "source/common/bytestream.cpp",
     "source/common/caniter.cpp",
     "source/common/chariter.cpp",
     "source/common/charstr.cpp",
     "source/common/cmemory.c",
     "source/common/cstring.c",
@@ skipping 163 matching lines @@
   direct_dependent_configs = [ ":icu_config" ]
 
   if (!is_win) {
     sources -= [ "source/stubdata/stubdata.c" ]
   }
 }
 
 if (is_win) {
   # On Windows the target DLL is pre-built so just use a copy rule.
   copy("icudata") {
-    external = true
     sources = [ "windows/icudt.dll" ]
     outputs = [ "$root_out_dir/icudt.dll" ]
   }
 } else {
   static_library("icudata") {
-    external = true
     sources = [
       # These are hand-generated, but will do for now.  The linux version is an
       # identical copy of the (mac) icudt46l_dat.S file, modulo removal of the
       # .private_extern and .const directives and with no leading underscore on
       # the icudt46_dat symbol.
       "android/icudt46l_dat.S",
       "linux/icudt46l_dat.S",
       "mac/icudt46l_dat.S",
     ]
     defines = [ "U_HIDE_DATA_SYMBOL" ]
 
     # TODO(brettw) support use_system_icu and icu_use_data_file_flag.
   }
 }