Use installed DBus libraries instead of generating them.

login_manager, power_manager, debugd and shill now expose a client
library with the generated dbus-proxies.h file and the system_api's
installed dbus-constants.h. This patch changes update_engine from
generating these DBus headers to use the installed client libraries.

The client libraries already include the service path string, so we
don't need to include system_api dbus-constants.h in most cases, unless
we actually use some parameter constants defined there.

BUG=b:23084776,b:23560718
TEST=./build_packages --board=link

Change-Id: Idb4501e784ebb5928c92902d114462be57d5826a
diff --git a/update_engine_client.cc b/update_engine_client.cc
index 6a88177..c6d4857 100644
--- a/update_engine_client.cc
+++ b/update_engine_client.cc
@@ -25,16 +25,14 @@
 #include <base/logging.h>
 #include <base/macros.h>
 #include <chromeos/daemons/dbus_daemon.h>
-#include <chromeos/dbus/service_constants.h>
 #include <chromeos/flag_helper.h>
 #include <dbus/bus.h>
+#include <update_engine/dbus-constants.h>
+#include <update_engine/dbus-proxies.h>
 
-#include "update_engine/dbus_constants.h"
-#include "update_engine/dbus-proxies.h"
-
-using chromeos_update_engine::kAttemptUpdateFlagNonInteractive;
-using chromeos_update_engine::kUpdateEngineServiceName;
 using std::string;
+using update_engine::kAttemptUpdateFlagNonInteractive;
+using update_engine::kUpdateEngineServiceName;
 
 namespace {