Fix a TODO in GN file

services/service_manager/background/BUILD.gn

 # Copyright 2016 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.
 
 group("background") {
   testonly = true
   deps = [
     ":lib",
   ]
 }
 
 source_set("lib") {
   sources = [
     "background_service_manager.cc",
     "background_service_manager.h",
   ]
   deps = [
     "//base",
     "//services/catalog:constants",
     "//services/catalog:lib",
     "//services/service_manager",
-    "//services/service_manager/public/cpp:sources",
+    "//services/service_manager/public/cpp",
     "//services/service_manager/runner:init",
     "//services/service_manager/runner/host:lib",
     "//services/service_manager/standalone",
   ]
 }