(I'm assuming that in your question, you used owner-lstsrv-l by way of
example only, and aren't actually receiving bounces for lstsrv-l, but
for some list which you host.)

You shouldn't have to alter sendmail aliases in order to remove error
messages.  Instead, you should alter your list configuration.  For one
thing, you could consider using Full-Auto in your auto-delete settings.
Something like:

* Auto-Delete= Full-Auto, Delay(0), Max(1)

You can also tell LISTSERV not to send errors to the list owner, but to
some other address:

* Errors-To= [log in to unmask]

although in general I'd agree with Valdis that it's better to fix errors
(or delete users who generate errors) than it is to /dev/null error
messages.  Unless you run massively large lists, auto-delete should work
fine to keep the number of errors at a manageable level.

Enjoy!

--
Liam