xmpp: Adapt to xmpp-parsers changes wrt autojoin

This attribute is now a simple bool instead of an enum.

parsers/ChangeLog

@@ -29,7 +29,9 @@ XXXX-YY-ZZ RELEASER <admin@example.com>
         `Option<Extensions>` instead of a `Vec<Element>`, to distinguish
         between it being absent or empty (!472).
       - Replace all boolean attributes with the `bool` type, so that we can
-        use them just like normal booleans (!476).
+        use them just like normal booleans. The following structs are deprecated:
+        pubsub::pubsub::Notify, bookmarks2::Autojoin, extdisco::Restricted,
+        fast::Tls0Rtt, legacy_omemo::IsPreKey, mam::Complete, sm::ResumeAttr (!476)
     * Improvements:
       - Keep unsupported vCard elements as `minidom::Element`, so that they
         get serialized back instead of being dropped.  We now also test for