remove left over principal selection
    
    https://fedorahosted.org/sssd/ticket/1303
    
    Domain start up was taking too long when there are many principals
    in a kerberos keytab. We were looking up in the keytab two times.
    
    The first time we try to select a proper principal and remember it.
    The second call happens almost right after the first one and
    it is just a check if the principal exists in the keytab, without
    any output information other than success/failure. It is
    probably a left over from https://fedorahosted.org/sssd/ticket/781.
    
    This patch removes the second call.