remote: convert struct push_cas to struct object_id

This gets rid of one use of get_sha1.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/remote.h b/remote.h
index 6c28cd3..2ecf4c8 100644
--- a/remote.h
+++ b/remote.h
@@ -282,7 +282,7 @@ struct ref *get_stale_heads(struct refspec *refs, int ref_count, struct ref *fet
 struct push_cas_option {
 	unsigned use_tracking_for_rest:1;
 	struct push_cas {
-		unsigned char expect[20];
+		struct object_id expect;
 		unsigned use_tracking:1;
 		char *refname;
 	} *entry;