pack-bitmap: convert khash_sha1 maps into kh_oid_map

All of the users of our khash_sha1 maps actually have a "struct
object_id". Let's use the more descriptive type.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/pack-bitmap.h b/pack-bitmap.h
index ee97922..00de3ec 100644
--- a/pack-bitmap.h
+++ b/pack-bitmap.h
@@ -51,7 +51,7 @@ int reuse_partial_packfile_from_bitmap(struct bitmap_index *,
 				       struct packed_git **packfile,
 				       uint32_t *entries, off_t *up_to);
 int rebuild_existing_bitmaps(struct bitmap_index *, struct packing_data *mapping,
-			     khash_sha1 *reused_bitmaps, int show_progress);
+			     kh_oid_map_t *reused_bitmaps, int show_progress);
 void free_bitmap_index(struct bitmap_index *);
 
 /*