OF-1141 Pubsub leaf nodes variant

This performs the same fix as for PEP, but this time on the PubSub services.

src/java/org/jivesoftware/openfire/pubsub/PubSubModule.java

@@ -427,7 +427,7 @@ public void initialize(XMPPServer server) {
             leafDefaultConfiguration.setNotifyDelete(true);
             leafDefaultConfiguration.setNotifyRetract(true);
             leafDefaultConfiguration.setPersistPublishedItems(false);
-            leafDefaultConfiguration.setMaxPublishedItems(-1);
+            leafDefaultConfiguration.setMaxPublishedItems(1);
             leafDefaultConfiguration.setPresenceBasedDelivery(false);
             leafDefaultConfiguration.setSendItemSubscribe(true);
             leafDefaultConfiguration.setSubscriptionEnabled(true);