archive.c: use OPT_BOOL()

archive.c: use OPT_BOOL()

The list variable (which is OPT_BOOLEAN) is initialized to 0 and only
checked against 0 in the code, so it is safe to use OPT_BOOL().

The worktree_attributes variable (which is OPT_BOOLEAN) is initialized to
0 and later assigned to a field with the same name in struct archive_args,
which is a bitfield of width 1. It is safe and even more correct to use
OPT_BOOL() here; the new test in 5001 demonstrates why using OPT_COUNTUP
is wrong.

Signed-off-by: Junio C Hamano <gitster@pobox.com>