Providing this information as plain text was doubtless worth the trouble ten years ago, but it seems likely that hardly anyone reads it in this format anymore. And the effort required to maintain these files (in the form of extra-complex markup rules in the relevant parts of the SGML documentation) is significant. So, let's stop doing that and rely solely on the other documentation formats. Per discussion, the plain-text INSTALL instructions might still be worth their keep, so we continue to generate that file. Rather than remove HISTORY and src/test/regress/README from distribution tarballs entirely, replace them with simple stub files that tell the reader where to find the relevant documentation. This is mainly to avoid possibly breaking packaging recipes that expect these files to exist. Back-patch to all supported branches, because simplifying the markup requirements for release notes won't help much unless we do it in all branches.
Per report from Colin 't Hart