Only advertise RSS feeds by default, not Atom
Advertising both is pointless, since every feed reader in the universe
supports both. Their functionality is essentially identical. And users
might be given a choice of multiple feeds to read when there's really
only one distinct feed. Plus, it cuts a line from the <head>. The Atom
feed still exists, and you can get the <head> link back if you really
want it with $wgAdvertisedFeedTypes.