hash: require hash algorithm in oidread() and oidclr()

Both `oidread()` and `oidclr()` use `the_repository` to derive the hash
function that shall be used. Require callers to pass in the hash
algorithm to get rid of this implicit dependency.

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

builtin/pack-objects.c

@@ -2078,7 +2078,8 @@ static void check_object(struct object_entry *entry, uint32_t object_index)
 				oidread(&base_ref,
 					use_pack(p, &w_curs,
 						 entry->in_pack_offset + used,
-						 NULL));
+						 NULL),
+					the_repository->hash_algo);
 				have_base = 1;
 			}
 			entry->in_pack_header_size = used + the_hash_algo->rawsz;