GN: Replace mojo/system.gni with forwarding groups

mojo/services/public/cpp/input_events/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")
-
 component("input_events") {
   deps = [
     "//base",
     "//ui/events",
     "//ui/gfx/geometry",
     "//mojo/environment:chromium",
+    "//mojo/public/c/system:for_component",
     "//mojo/services/public/interfaces/input_events",
     "//mojo/services/public/interfaces/geometry",
     "//mojo/services/public/cpp/geometry",
   ]
-  deps += mojo_system_for_component
 
   defines = [
     "MOJO_INPUT_EVENTS_IMPLEMENTATION",
   ]
 
   sources = [
     "lib/input_events_type_converters.cc",
     "lib/input_events_type_converters.h",
     "lib/mojo_extended_key_event_data.cc",
     "lib/mojo_extended_key_event_data.h",
     "input_events_type_converters.h",
     "mojo_input_events_export.h",
   ]
 }