man-db: wrap groff instead of compiling in

Some manpages, e.g. `systemd.time` were broken in a way that they
were rendered from the beginning after part of the page, and then only
lasted for maybe a third of their length.

So we just add groff in the wrapper instead of the configure phase like
every other distribution seems to do, and that fixes it.
Patch by @Mic92.

Fixes #19323.