Drop the ronn source files, check in the generated files instead. This gets rid
of the ruby+gem+ronn toolchain requirement at the cost of having to edit raw man
pages.
ronn files are as-generated but with the preamble and generation date removed.
The latter isn't important enough to keep, it'll just go stale for manually
maintained files and it's not worth setting up a configure_file() just for that
date.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>