This reverts commit 3e7649f01b.
turns out that home-manager depends on it, and restoring this patch for
now seems preferrable to breaking home-manager until they move away from
docbook for their manpage generation.
we're no longer using docbook to render the manpages, so we don't need
this patch for our manuals to be usable. remove it to reduce the diff
between nixos and other distros for this package.