Revert "OF-2921: Prevent deadlock by not broadcasting synchronously"

This reverts commit b8b5713.

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.

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

@@ -291,9 +291,7 @@ 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);
@@ -1362,9 +1360,7 @@ public void onConnectionClose(Object handback) {
                         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);