[d8] Remove "os" object from d8.

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/mips.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 
 if (is_android) {
@@ skipping 1822 matching lines @@
 
     deps = [
       ":d8_js2c",
       ":v8",
       ":v8_libplatform",
       "//build/config/sanitizers:deps",
     ]
 
     # TODO(jochen): Add support for vtunejit.
 
-    if (is_posix) {
-      sources += [ "src/d8-posix.cc" ]
-    } else if (is_win) {
-      sources += [ "src/d8-windows.cc" ]
-    }
-
     if (!is_component_build) {
       sources += [
         "$target_gen_dir/d8-js.cc",
       ]
     }
     if (v8_enable_i18n_support) {
       deps += [ "//third_party/icu" ]
     }
   }
 }