Remove --promise-extra flag

BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/dcheck_always_on.gni")
 import("//build/config/mips.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 
@@ skipping 413 matching lines @@
   ]
 
   # NOSORT
   sources = [
     "src/js/macros.py",
     "src/messages.h",
     "src/js/harmony-async-await.js",
     "src/js/harmony-atomics.js",
     "src/js/harmony-simd.js",
     "src/js/harmony-string-padding.js",
-    "src/js/promise-extra.js",
   ]
 
   outputs = [
     "$target_gen_dir/experimental-libraries.cc",
   ]
 
   if (v8_enable_i18n_support) {
     sources += [
       "src/js/icu-case-mapping.js",
       "src/js/intl-extra.js",
@@ skipping 2130 matching lines @@
 
   deps = [
     ":fuzzer_support",
   ]
 
   configs = [ ":internal_config" ]
 }
 
 v8_fuzzer("wasm_asmjs_fuzzer") {
 }