GN: Replace mojo/system.gni with forwarding groups

mojo/apps/js/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("//mojo/system.gni")
-
 shared_library("mojo_js") {
   sources = [
     "application_delegate_impl.cc",
     "js_app.cc",
     "mojo_module.cc",
     "main.cc"
   ]
 
   deps = [
     ":js",
     "//base:i18n",
     "//mojo/application",
+    "//mojo/public/c/system:for_shared_library",
     "//mojo/public/cpp/bindings",
     "//mojo/public/cpp/utility",
     "//mojo/services/public/interfaces/content_handler",
-  ] + mojo_system_for_shared_library
+  ]
 }
 
 # GYP version: part of mojo/mojo_apps.gypi:mojo_js_lib
 source_set("js") {
   deps = [
     "//base",
     "//gin",
     "//mojo/apps/js/bindings",
     "//mojo/apps/js/bindings/gl",
     "//mojo/bindings/js",
     "//v8",
   ]
   sources = [
     "mojo_runner_delegate.cc",
     "mojo_runner_delegate.h",
   ]
 }