object-file: stop using the_hash_algo

There are a couple of users of the `the_hash_algo` macro, which
implicitly depends on `the_repository`. Adapt these callers to not do so
anymore, either by deriving it from already-available context or by
using `the_repository->hash_algo`. The latter variant doesn't yet help
to remove the global dependency, but such users will be adapted in the
following commits to not use `the_repository` anymore.

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

object-file.h

@@ -89,6 +89,7 @@ typedef int each_loose_subdir_fn(unsigned int nr,
 				 void *data);
 int for_each_file_in_obj_subdir(unsigned int subdir_nr,
 				struct strbuf *path,
+				const struct git_hash_algo *algo,
 				each_loose_object_fn obj_cb,
 				each_loose_cruft_fn cruft_cb,
 				each_loose_subdir_fn subdir_cb,