GKLeaderboardViewControllerDelegate has been supplanted by the more general GKGameCenterControllerDelegate, which includes support for Achievements and Challenges as well as Leaderboards.
To summarize:
// the following are DEPRECATED as of iOS 7.0:
// GKLeaderboardViewController [DEPRECATED as of iOS 7.0]
// GKLeaderboardViewControllerDelegate [DEPRECATED as of iOS 7.0], with its one required method …