GN: Replace mojo/system.gni with forwarding groups

mojo/services/view_manager/BUILD.gn

Index: mojo/services/view_manager/BUILD.gn
diff --git a/mojo/services/view_manager/BUILD.gn b/mojo/services/view_manager/BUILD.gn
index 9f0bb82384064fb3fb0ee9480be3d9c7e6f7acc4..21b2796638cf08c7d0acf4033ede994c85cd2f0c 100644
--- a/mojo/services/view_manager/BUILD.gn
+++ b/mojo/services/view_manager/BUILD.gn
@@ -2,8 +2,6 @@
 # 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 = [
@@ -12,6 +10,7 @@ component("view_manager") {
     "//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",
@@ -26,7 +25,7 @@ component("view_manager") {
     "//ui/events:events_base",
     "//ui/gfx",
     "//ui/gfx/geometry",
-  ] + mojo_system_for_component
+  ]
 
   defines = [
     "MOJO_VIEW_MANAGER_IMPLEMENTATION",