GN: Replace mojo/system.gni with forwarding groups

mojo/services/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
 component("view_manager") {
   deps = [
     "//base",
     "//cc/surfaces",
     "//mojo/application",
     "//mojo/common",
     "//mojo/environment:chromium",
+    "//mojo/public/c/system:for_component",
     "//mojo/services/public/cpp/geometry",
     "//mojo/services/public/cpp/input_events",
     "//mojo/services/public/cpp/surfaces",
     "//mojo/services/public/cpp/view_manager:common",
     "//mojo/services/public/interfaces/geometry",
     "//mojo/services/public/interfaces/input_events",
     "//mojo/services/public/interfaces/native_viewport",
     "//mojo/services/public/interfaces/surfaces",
     "//mojo/services/public/interfaces/view_manager",
     "//ui/base",
     "//ui/events",
     "//ui/events:events_base",
     "//ui/gfx",
     "//ui/gfx/geometry",
-  ] + mojo_system_for_component
+  ]
 
   defines = [
     "MOJO_VIEW_MANAGER_IMPLEMENTATION",
   ]
 
   sources = [
     "access_policy.h",
     "access_policy_delegate.h",
     "connection_manager.cc",
     "connection_manager.h",
@@ skipping 38 matching lines @@
     "//mojo/system",
     "//testing/gtest",
   ]
 
   sources = [
     "test_change_tracker.cc",
     "test_change_tracker.h",
     "view_manager_unittest.cc",
   ]
 }