Ticket #47581 - Winsync plugin segfault during incremental backoff
    
    Bug description: Once WinSync backoff timer is set, even if the
    protocol that the backoff timer belongs to is deleted by removing
    the windows sync agreement, the timer is not deleted from the event
    queue.  Thus the timer is expired and backoff is called, it crashes
    the server since the protocol handle is already freed, then.
    
    Fix description: Make sure to delete the backoff timer when
    1) a windows sync agreement is removed and the protocol is deleted, and
    2) a new backoff timer set and there is already a backoff timer set up.
    
    https://fedorahosted.org/389/ticket/47581
    
    Reviewed by rmeggins (Thank you, Rich!!)
    (cherry picked from commit d70e66b2157ce3ba40c5e1cb074c2d5c150ddc5b)