fsck: don't require an object struct for report()

fsck: don't require an object struct for report()

The report() function really only cares about the oid and type of the
object, not the full object struct. Let's convert it to take those two
items separately, which gives our callers more flexibility.

This makes some already-long lines even longer. I've mostly left them,
as our eventual goal is to shrink these down as we continue refactoring
(e.g., "&item->object" becomes "&item->object.oid, item->object.type",
but will eventually shrink down to "oid, type").

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