buffet: Simplify device registration.

Make device always finalize registration ticket itself.

Also minor unifications in the code.

BUG=None
TEST=cros_work_make buffet --test

Change-Id: I7aa432aee2546fd562fd7048ef320d773c32be19
Reviewed-on: https://chromium-review.googlesource.com/220380
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Anton Muhin <antonm@chromium.org>
Tested-by: Anton Muhin <antonm@chromium.org>
diff --git a/buffet/manager.h b/buffet/manager.h
index a56b6c3..4648b95 100644
--- a/buffet/manager.h
+++ b/buffet/manager.h
@@ -52,8 +52,7 @@
                                         const std::map<std::string,
                                                        std::string>& params);
   // Handles calls to org.chromium.Buffet.Manager.FinishRegisterDevice().
-  std::string HandleFinishRegisterDevice(chromeos::ErrorPtr* error,
-                                         const std::string& user_auth_code);
+  std::string HandleFinishRegisterDevice(chromeos::ErrorPtr* error);
   // Handles calls to org.chromium.Buffet.Manager.UpdateState().
   void HandleUpdateState(chromeos::ErrorPtr* error,
                          const chromeos::VariantDictionary& property_set);