GN: Replace mojo/system.gni with forwarding groups

mojo/services/public/cpp/view_manager/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: mojo/mojo_services.gypi:mojo_view_manager_lib
 source_set("view_manager") {
   sources = [
     "lib/bitmap_uploader.cc",
     "lib/bitmap_uploader.h",
     "lib/view.cc",
     "lib/view_manager_client_factory.cc",
     "lib/view_manager_client_impl.cc",
     "lib/view_manager_client_impl.h",
     "lib/view_observer.cc",
     "lib/view_private.cc",
     "lib/view_private.h",
     "view.h",
     "view_manager.h",
     "view_manager_client_factory.h",
     "view_manager_delegate.h",
     "view_observer.h",
     "window_manager_delegate.h",
   ]
 
   deps = [
     ":common",
     "//base",
     "//cc/surfaces",
     "//gpu",
     "//mojo/application",
+    "//mojo/public/gles2:for_shared_library",
     "//mojo/public/interfaces/application",
     "//mojo/services/public/cpp/geometry",
     "//mojo/services/public/cpp/surfaces",
     "//mojo/services/public/interfaces/geometry",
     "//mojo/services/public/interfaces/gpu",
     "//mojo/services/public/interfaces/view_manager",
     "//mojo/services/public/interfaces/window_manager",
     "//skia",
     "//ui/events",
     "//ui/gfx",
     "//ui/gfx/geometry",
-  ] + mojo_gles2_for_shared_library
+  ]
 
   forward_dependent_configs_from = [ "//skia" ]
 }
 
 source_set("common") {
   sources = [
     "types.h"
   ]
 }