Merge //ios/chrome/browser/signin:{authentication_service,signin}.

ios/chrome/browser/signin/authentication_service_unittest.mm

Index: ios/chrome/browser/signin/authentication_service_unittest.mm
diff --git a/ios/chrome/browser/signin/authentication_service_unittest.mm b/ios/chrome/browser/signin/authentication_service_unittest.mm
index 2491df4a41fd07cb8b4bc296aee4c0f6753984bd..ff4f8d14dabe81b15394ad20a6f6781e16e89330 100644
--- a/ios/chrome/browser/signin/authentication_service_unittest.mm
+++ b/ios/chrome/browser/signin/authentication_service_unittest.mm
@@ -135,7 +135,6 @@ class AuthenticationServiceTest : public PlatformTest,
     std::unique_ptr<syncable_prefs::PrefServiceSyncable> prefs =
         factory.CreateSyncable(registry.get());
     RegisterBrowserStatePrefs(registry.get());
-    AuthenticationService::RegisterPrefs(registry.get());
     return prefs;
   }