Make optional the javax.xml.rpc.api module dependency added to deployments by EjbDependencyDeploymentUnitProcessor

EjbDependencyDeploymentUnitProcessor add a module dep on the javax.xml.rpc.api module to all deployments. This really just supports a single method in the SessionContext interface, a method that isn't really usable anyway as we don't support JAX RPC. The method is gone in EE 9 and we won't even provide the API jar in our EE 9 dist, so make this module dep optional so if this code runs in an EE 9 context it just works.