treewide: drop uses of `for_each_{loose,packed}_object()`

treewide: drop uses of `for_each_{loose,packed}_object()`

We're using `for_each_loose_object()` and `for_each_packed_object()` at
a couple of callsites to enumerate all loose and packed objects,
respectively. These functions will be removed in a subsequent commit in
favor of the newly introduced `odb_source_loose_for_each_object()` and
`packfile_store_for_each_object()` replacements.

Prepare for this by refactoring the sites accordingly.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>