CHANGES: rename to CHANGES.md, no longer generated

- scripts/log2changes.pl was not included in release tarballs, which broke
  reproducible builds

- since log2changes uses git to generate the contents, it makes it difficult
  to generate the same contents later (it would need to be fixed)

- the CHANGES file has outlived its purpose. the main changes are in the
  RELEASE-NOTES, the rest are better tracked directly using git or on GitHub

- put a fixed CHANGES.md in there instead pointing out where the info lives
  now

Closes #14331

packages/OS400/makefile.sh

@@ -65,7 +65,7 @@ fi
 #       Copy some documentation files if needed.
 
 for TEXT in "${TOPDIR}/COPYING" "${SCRIPTDIR}/README.OS400"             \
-    "${TOPDIR}/CHANGES" "${TOPDIR}/docs/THANKS" "${TOPDIR}/docs/FAQ"    \
+    "${TOPDIR}/CHANGES.md" "${TOPDIR}/docs/THANKS" "${TOPDIR}/docs/FAQ"    \
     "${TOPDIR}/docs/FEATURES" "${TOPDIR}/docs/SSLCERTS.md"              \
     "${TOPDIR}/docs/RESOURCES" "${TOPDIR}/docs/VERSIONS.md"             \
     "${TOPDIR}/docs/HISTORY.md"