Section "4.2. Clustered Singleton MDBs" in the Development Guide for EJBs needs updating

Step 2 is no longer necessary:
In your MDB class, use the @org.jboss.ejb3.annotation.ClusteredSingleton

See this section in the community migration guide for details:

https://docs.jboss.org/author/display/WFLY10/How+do+I+migrate+my+application+from+AS7+to+WildFly#HowdoImigratemyapplicationfromAS7toWildFly-StatefulSessionEJBClustering