ref-filter: drop unused "obj" parameters

ref-filter: drop unused "obj" parameters

The grab_person() and grab_sub_body_contents() functions take both an
object struct and a buf/sz pair of the object bytes. However, they use
only the latter, since "struct object" does not contain the parsed ident
(nor the whole commit message, of course).

Let's get rid of these misleading "struct object" parameters. It's
possible we may want them in the future (e.g., to generate error
messages that mention the object id), but since these are static
functions, we can easily add them back in later (and if we do want that
information, it's likely we'd pass it through a more generalized
"parsing context" struct anyway).

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