Pass struct archiver and struct archiver_args explicitly to parse_archive_args
and remove the latter from the former.  This allows us to get rid of struct
archiver_desc and simplifies the code a bit.
Signed-off-by: NRene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>