Remove unused method in pubsub.Subscription

smack-extensions/src/main/java/org/jivesoftware/smackx/pubsub/Subscription.java

@@ -150,12 +150,4 @@ public class Subscription extends NodeExtension {
         return builder;
     }
 
-    private static void appendAttribute(StringBuilder builder, String att, String value) {
-        builder.append(' ');
-        builder.append(att);
-        builder.append("='");
-        builder.append(value);
-        builder.append('\'');
-    }
-
 }