Deprecating libXp

[Alan Coopersmith]

As Demi Marie pointed out in
https://gitlab.freedesktop.org/xorg/lib/libxp/-/issues/1
it's not really practical to actually use this library since we killed
off Xprt years ago.  But it still seems to be pretty widely shipped:
   https://repology.org/project/libxp/versions
Though some distros have dropped it already:
   https://repology.org/project/libxp/history
I imagine more will do so if we actually tell them they should

So I'm proposing we add the following statement to the README for libXp
and include it in a release I'll make once we've agreed on the text:

   This library provides support for X11 clients to print via the X Print
   Extension, as previously implemented in the Xprt server.  X.Org removed
   support for the Xprt server from the xorg-server releases in the 1.6.0
   release in 2009, and the standalone git repo it was moved to has been
   unmaintained since 2009, making it difficult to actually use this library.

   While X.Org has continued to maintain this library for binary compatibility,
   we do not plan to do so for the long term and encourage anyone still building
   or shipping it to investigate how to stop doing so going forward as we now
   consider it to be deprecated.

I've filed a gitlab MR for discussion there as well:
https://gitlab.freedesktop.org/xorg/lib/libxp/-/merge_requests/5

(I'm taking extra time off around the US Labor Day holiday next weekend,
  so will likely merge this and release after that.)

-- 
         -Alan Coopersmith-                 alan.coopersmith at oracle.com
          Oracle Solaris Engineering - https://blogs.oracle.com/solaris