The recipe for making a man page from .texi is duplicated several
times over.  Capture it in suitable pattern rules instead.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20170113144135.5150-20-marcandre.lureau@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>