Do you mean RDF/RSS 1.0 feed?
It is not deprecated and should be available just fine at /feed/rdf
To force RSS 2.0 links to use RSS 0.92 template try this:
remove_action( 'do_feed_rss2', 'do_feed_rss2' );
add_action( 'do_feed_rss2', 'do_feed_rss' );