Support of Three20 has been discontinued.
If you updated to this revision by accident (e.g. a git pull), you might want to switch back to the
version you had before (git checkout cc672132ab).
Three20 still compiles and seems to work on iOS6, so there's no immediate need to remove everything now. Still, as the library is not maintained anymore, it might be a good time to replace it.
Lots of Three20's helpers are not needed anymore, as they are now present right in iOS. For other parts there are some really good replacement available. If you're searching for a full replacement, [NimbusKit][http://nimbuskit.info] might help, they even provide a [migration guide][http://wiki.nimbuskit.info/Three20-Migration-Guide].
[Three20 Mailing List][http://groups.google.com/group/three20/]
[Three20 Tagged Questions on StackOverflow][http://stackoverflow.com/questions/tagged/three20]