receive-pack: fix funny ref error messsage

receive-pack: fix funny ref error messsage

When the user deletes the remote one level branch through
"git push origin -d refs/foo", remote will return an error:
"refusing to create funny ref 'refs/foo' remotely", here we
are not creating "refs/foo" instead wants to delete it, so a
better error description here would be: "refusing to update
funny ref 'refs/foo' remotely".

Signed-off-by: ZheNing Hu <adlternative@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>