GN: Replace mojo/system.gni with forwarding groups

mojo/examples/aura_demo/BUILD.gn

Index: mojo/examples/aura_demo/BUILD.gn
diff --git a/mojo/examples/aura_demo/BUILD.gn b/mojo/examples/aura_demo/BUILD.gn
index 70ca8db2c957d2f001c35b279ca2470b1f88ca61..ba2fc37599cc58aca316e76ab9bde277809c79e0 100644
--- a/mojo/examples/aura_demo/BUILD.gn
+++ b/mojo/examples/aura_demo/BUILD.gn
@@ -3,7 +3,6 @@
 # found in the LICENSE file.
 
 import("//build/config/ui.gni")
-import("//mojo/system.gni")
 
 assert(use_aura)
 
@@ -26,10 +25,11 @@ shared_library("mojo_aura_demo") {
     "//mojo/application",
     "//mojo/common",
     "//mojo/aura",
+    "//mojo/public/c/system:for_shared_library",
     "//mojo/services/public/interfaces/geometry",
     "//mojo/services/public/cpp/geometry",
     "//mojo/services/public/cpp/view_manager",
-  ] + mojo_system_for_shared_library
+  ]
 
   datadeps = [ ":init" ]
 }
@@ -45,6 +45,7 @@ shared_library("init") {
   deps = [
     "//base",
     "//mojo/application",
+    "//mojo/public/c/system:for_shared_library",
     "//mojo/services/public/interfaces/view_manager",
-  ] + mojo_system_for_shared_library
+  ]
 }