Remove a bunch of antique information from the appendix in the docs

Remove a bunch of antique information from the appendix in the docs
that discusses CVS. Remove the recommendation to use cvs 1.10. Remove
discussion of alleged CVSup binaries on postgresql.org, because they
have not existed for several years. Remove discussion of how to
build cvsup from source because the existing text is outdated, and
more accurate information is available from the CVSup homepage.