OF-2921: Partial revert of b98a83d

Routing the unavailable presence that's sent out when a session closes cannot be made asynchronous. If the 'next step' is done prior to the routing of unavailable presence having completed, the session seems to be (partially) re-added. This causes an invalid state: the routing table no longer has the session, but caches such as the Routing Users Cache does.

This incorrect behavior was introduced by a fix for OF-2921: b98a83d

It was already partially reverted by 7aca93f

This commit reverts the remainder.

xmppserver/src/main/java/org/jivesoftware/openfire/SessionManager.java

@@ -292,9 +292,7 @@ public synchronized void terminateDetached(LocalSession session) {
                     Presence presence = new Presence();
                     presence.setType(Presence.Type.unavailable);
                     presence.setFrom(session.getAddress());
-
-                    // Broadcast asynchronously, to reduce the likelihood of the broadcast introducing a deadlock (OF-2921).
-                    TaskEngine.getInstance().submit(() -> router.route(presence));
+                    router.route(presence);
                 }
 
                 session.getStreamManager().onClose(router, serverAddress);