Drop pre-generated man pages from release tarballs

[pmatilai]

We've traditionally bundled these because it was not a big deal when source tarballs were something one needed to build anyhow, but this is no longer the case and actually hurts us.

We currently do this because our man pages are generated by Pandoc, which is a terrible build dependency to have for something as core-level as rpm is. That needs to be changed first (#3563)