macros: Remove backwards-compatibility variants introduced in the previous commit.

src/blocking.rs

@@ -41,7 +41,7 @@ macro_rules! generate_blocking_element {
                     check_self!(child, "item", BLOCKING);
                     check_no_unknown_attributes!(child, "item", ["jid"]);
                     check_no_children!(child, "item");
-                    items.push(get_attr!(child, "jid", required));
+                    items.push(get_attr!(child, "jid", Required));
                 }
                 Ok($elem { items })
             }