am: mark unused keep_cr parameters

am: mark unused keep_cr parameters

When parsing the input, we have a "keep_cr" parameter to tell us how to
handle line endings. But this doesn't apply to stgit or hg patches
(which are not mailbox formats where we have to worry about that), so we
ignore the parameter entirely in those functions.

Let's mark these as unused so that -Wunused-parameter does not complain
about them.

Note that we could just drop these parameters entirely. They are
necessary to conform to the mail_conv_fn interface used by
split_mail_conv(), but these two callbacks are the only ones used with
that function. The other formats (which _do_ care about keep_cr) use
split_mail_mbox(). But it's conceivable that we'd eventually add another
format that does care about this option, so let's leave it as part of
the generic interface.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>