The retired flag is private to the backend,
which obeys it when selecting nodeids.
But do_list works off the nodeids in a Multilink., so
the backend has no opportunity to intervene (that is,
hide the retired items).

Perhaps a Multilink *should* show retired items that
are still linked-to. But that means that (1) you should
be able to "unretire" an item, and that (2) there should
be the ability to "retire that doggy and take him out
of my Multilink".

The other way would be to add a 
Class.is_retired(nodeid) 
method, and make htmltemplate do the test.