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/connection_manager.cc b/connection_manager.cc
index 2589a4a..99dbcb1 100644
--- a/connection_manager.cc
+++ b/connection_manager.cc
@@ -21,10 +21,10 @@
 
 #include <base/stl_util.h>
 #include <base/strings/string_util.h>
-#include <chromeos/dbus/service_constants.h>
 #include <policy/device_policy.h>
+#include <shill/dbus-constants.h>
+#include <shill/dbus-proxies.h>
 
-#include "shill/dbus-proxies.h"
 #include "update_engine/prefs.h"
 #include "update_engine/system_state.h"
 #include "update_engine/utils.h"