pack-objects: swap 'show_{object,commit}_pack_hint'

pack-objects: swap 'show_{object,commit}_pack_hint'

show_commit_pack_hint() has heretofore been a noop, so its position
within its compilation unit only needs to appear before its first use.

But the following commit will sometimes have `show_commit_pack_hint()`
call `show_object_pack_hint()`, so reorder the former to appear after
the latter to minimize the code movement in that patch.

Suggested-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>