builtin/repack.c: avoid using hash_to_hex() in pack geometry

In previous commits, we started passing either repository or
git_hash_algo pointers around to various spots within builtin/repack.c
to reduce our dependency on the_repository in the hope of undef'ing
USE_THE_REPOSITORY_VARIABLE.

This commit takes us as far as we can (easily) go in that direction by
removing the only use of a convenience function that only exists when
USE_THE_REPOSITORY_VARIABLE is defined.

Unfortunately, the only other such function is "is_bare_repository()",
which is less than straightforward to convert into, say,
"repo_is_bare()", the latter of the two accepting a repository pointer.

Punt on that for now, and declare this commit as the stopping point for
our efforts in the direction of undef'ing USE_THE_REPOSITORY_VARIABLE.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: ttaylorr

builtin/repack.c

@@ -683,12 +683,14 @@ static void geometry_remove_redundant_packs(struct pack_geometry *geometry,
 					    struct string_list *names,
 					    struct existing_packs *existing)
 {
+	const struct git_hash_algo *algop = existing->repo->hash_algo;
 	struct strbuf buf = STRBUF_INIT;
 	uint32_t i;
 
 	for (i = 0; i < geometry->split; i++) {
 		struct packed_git *p = geometry->pack[i];
-		if (string_list_has_string(names, hash_to_hex(p->hash)))
+		if (string_list_has_string(names, hash_to_hex_algop(p->hash,
+								    algop)))
 			continue;
 
 		strbuf_reset(&buf);