@SessionScoped EJBs are replicating proxy placeholders unnecessarily

As part of WFLY-17217, EJB proxies were meant to be treated as immutable by the session manager. Currently, the service loader annotation of org.jboss.as.ejb3.component.stateful.StatefulSessionBeanImmutability is commented out, which prevents the session manager from loading its Immutability implementation.
This was temporarily disabled during local testing and its exclusion was not intentional.