remote: convert get_stale_heads to take a struct refspec

Convert 'get_stale_heads()' to take a 'struct refspec' as a parameter instead
of a list of 'struct refspec_item'.

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 5e46df7..3fad1f0 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -963,7 +963,7 @@ static int prune_refs(struct refspec *rs, struct ref *ref_map,
 		      const char *raw_url)
 {
 	int url_len, i, result = 0;
-	struct ref *ref, *stale_refs = get_stale_heads(rs->items, rs->nr, ref_map);
+	struct ref *ref, *stale_refs = get_stale_heads(rs, ref_map);
 	char *url;
 	int summary_width = transport_summary_width(stale_refs);
 	const char *dangling_msg = dry_run