Remove ZERO_STRUCT() call
    
    ipa_sam uses Samba's macro ZERO_STRUCT() to safely zero out a block in
    memory. On F30 ZERO_STRUCT() is currently broken, because it uses the
    undefined C11 function memset_s().
    
    During investigation of the bug, it turned out that
    ZERO_STRUCT(td->security_identifier) is not needed. The whole td struct
    is allocated with talloc_zero(), so td->security_identifier is already
    zeroed.
    
    See: https://bugzilla.redhat.com/show_bug.cgi?id=1672231
    Signed-off-by: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>