ldap: remove originalMeberOf if there is no memberOf
    
    Since originalMemerberOf is not mapped directly to an original attribute
    and is handled specially it is not automatically removed if there is no
    memberOf in the original object anymore. This patch put
    originalMemerberOf on the list of attribute which should be removed in
    that case.
    
    Resolves https://fedorahosted.org/sssd/ticket/2917
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>
    (cherry picked from commit 9a2f018c0f68a3ada4cea4128a861a7f85893f22)