Delete friend requests

Each DeleteFriendRequest must contain both the applicant's and recipient's user IDs.

DeleteFriendRequest *request =
    [[DeleteFriendRequest alloc] initWithFromUserID:application.fromUserID
                                          toUserID:application.toUserID];
[[OIMManager manager] deleteFriendRequests:@[request]
                                 onSuccess:nil
                                 onFailure:nil];

A successful callback means that the delete request has completed. It does not create or remove a friend relationship. Other clients may still merge the incremental update through the friend-request deletion delegate. Reset pagination and query again when reconciliation is needed.