Drop unused v8 config var from chromium config

build/common.gypi

 # 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 1395 matching lines @@
     # Whether we are using the rlz library or not.  Platforms like Android send
     # rlz codes for searches but do not use the library.
     'enable_rlz%': 0,
 
     # Turns on the i18n support in V8.
     'v8_enable_i18n_support': 1,
 
     # Compile d8 for the host toolset.
     'v8_toolset_for_d8': 'host',
 
-    # Compiles v8 without its platform library.
-    'v8_use_default_platform': 0,
-
     # Use the chromium skia by default.
     'use_system_skia%': '0',
 
     # Use brlapi from brltty for braille display support.
     'use_brlapi%': 0,
 
     # Relative path to icu.gyp from this file.
     'icu_gyp_path': '../third_party/icu/icu.gyp',
 
     # IPC fuzzer is disabled by default.
@@ skipping 4225 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }