GN: Replace mojo/system.gni with forwarding groups

media/mojo/services/BUILD.gn

Index: media/mojo/services/BUILD.gn
diff --git a/media/mojo/services/BUILD.gn b/media/mojo/services/BUILD.gn
index 2288fb6f23dfb047338d0819b3c67f8bfff19546..1ad6846f07374fd8db0b34851b1ac822a561f5cd 100644
--- a/media/mojo/services/BUILD.gn
+++ b/media/mojo/services/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: media/media.gyp:mojo_media_lib
 source_set("lib") {
   deps = [
@@ -12,10 +10,9 @@ source_set("lib") {
     "//media/mojo/interfaces"
     "//mojo/common",
     "//mojo/environment:chromium",
+    "//mojo/public/c/system:for_component",
   ]
 
-  deps += mojo_system_for_component
-
   sources = [
     "media_type_converters.cc",
     "media_type_converters.h",