sync: remove GetAuthenticatedUsername from ProfileSyncService/SyncBackendHost.

chrome/browser/sync/glue/sync_backend_host.h

Index: chrome/browser/sync/glue/sync_backend_host.h
diff --git a/chrome/browser/sync/glue/sync_backend_host.h b/chrome/browser/sync/glue/sync_backend_host.h
index 81af6a9233ff88d35d888a2dde10ef4a6d9fb14b..9b00cc61392864f13a4a35d34726747868b230f7 100644
--- a/chrome/browser/sync/glue/sync_backend_host.h
+++ b/chrome/browser/sync/glue/sync_backend_host.h
@@ -235,11 +235,6 @@ class SyncBackendHost {
     return sync_data_folder_path_;
   }
 
-  // Returns the authenticated username of the sync user, or empty if none
-  // exists. It will only exist if the authentication service provider (e.g
-  // GAIA) has confirmed the username is authentic.
-  string16 GetAuthenticatedUsername() const;
-
   // Determines if the underlying sync engine has made any local changes to
   // items that have not yet been synced with the server.
   // ONLY CALL THIS IF OnInitializationComplete was called!