Remove unused remote_prefix member in builtin-remote

Not sure when this became unused, but no code references it,
other than to populate the strbuf with an initial value.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-remote.c

@@ -206,7 +206,6 @@ static void read_branches(void)
 
 struct ref_states {
 	struct remote *remote;
-	struct strbuf remote_prefix;
 	struct path_list new, stale, tracked;
 };
 
@@ -262,8 +261,6 @@ static int get_ref_states(const struct ref *ref, struct ref_states *states)
 	}
 	free_refs(fetch_map);
 
-	strbuf_addf(&states->remote_prefix,
-		"refs/remotes/%s/", states->remote->name);
 	for_each_ref(handle_one_branch, states);
 	sort_path_list(&states->stale);