SSL README

I notice that there is a src/backend/libpq/README.SSL that contains a
couple of copied emails in it (it even contains our end-of-broadcast
message string!) And it contains a reply to the mail, with quoted stuff!

In general, this seem to be some hints about how to use things. Things
that if we need them at all, should go in the main manual. It's
certainly not code documentation, so it should not go in a README file
in the sourcetree.

My suggestion is to just get rid of any enduser docs from that one, and
possibly add stuff to the main manual once we feel it's needed. The part
that documents the SSL "negotiation protocol inside libpq" should stay,
of course.

Any objections?

//Magnus