Drop use of ronn, switch to raw roff instead

Drop use of ronn, switch to raw roff instead

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>