AI: checking on use of NAPTR metadata material

["Cantor, Scott" <cantor.2@osu.edu>]

I checked with Peter, and he informs me that Neustar does have deployments
of that spec, so we obviously won't be removing it outright. I favor
moving it to an extension document packaged with the spec, but I think
we'll have to discuss it. Obviously we want to slim down the key documents
as much as we can, while retaining essential material that probably will
be added to in this round of work.

-- Scott