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 813e0f0fb19f1678aa4c9bd0198e4053b7b7f7ee..7883228d66273b08982c26da8796048c1cfe2f72 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!