list-objects: drop name_path entirely

In the previous commit, we left name_path as a thin wrapper
around a strbuf. This patch drops it entirely. As a result,
every show_object_fn callback needs to be adjusted. However,
none of their code needs to be changed at all, because the
only use was to pass it to path_name(), which now handles
the bare strbuf.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

pack-bitmap-write.c

@@ -148,7 +148,7 @@ static uint32_t find_object_pos(const unsigned char *sha1)
 	return entry->in_pack_pos;
 }
 
-static void show_object(struct object *object, const struct name_path *path,
+static void show_object(struct object *object, struct strbuf *path,
 			const char *last, void *data)
 {
 	struct bitmap *base = data;