Make sure your web server returns a 404 for deleted resources.
That is enough.
From the official Google Web Master Central blog:
Q: Do the 404 errors reported in Webmaster Tools affect my site’s
A: 404s are a perfectly normal part of the web; the Internet
is always changing, new content is born, old content dies, and when it
dies it (ideally) returns a 404 HTTP response code. Search engines are
aware of this; we have 404 errors on our own sites, as you can see
above, and we find them all over the web. In fact, we actually prefer
that, when you get rid of a page on your site, you make sure that it
returns a proper 404 or 410 response code (rather than a “soft 404”).
Keep in mind that in order for our crawler to see the HTTP response
code of a URL, it has to be able to crawl that URL—if the URL is
blocked by your robots.txt file we won’t be able to crawl it and see
its response code. The fact that some URLs on your site no longer
exist / return 404s does not affect how your site’s other URLs (the
ones that return 200 (Successful)) perform in our search results.