GN: Replace mojo/system.gni with forwarding groups

mojo/apps/js/bindings/gl/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")
-
 # GYP version: part of mojo/mojo_apps.gypi:mojo_js_lib
 source_set("gl") {
   deps = [
     "//base",
     "//gin",
     "//v8",
+    "//mojo/environment:chromium",
+    "//mojo/public/gles2:for_shared_library",
     "//mojo/services/gles2:bindings",
-    "//mojo/environment:chromium",
-  ] + mojo_gles2_for_shared_library
+  ]
 
 
   sources = [
     "context.cc",
     "context.h",
     "module.cc",
     "module.h",
   ]
 }