RE: 'prospero' scheme status and draft

I think the policy issues around 'obsolete' and 'historic' for
documents are tricky, and we're not likely to make good progress
on the topic on 'uri@w3.org'.

I suggest we focus on updating the documents themselves to
'speak the truth'.

So let's update the 'prospero' document to stay that prospero
is an obsolete protocol.

If the IESG decides that it's unnecessary to have a document
just to say that, then we can just drop the draft.

Larry