Revert "Don't cast"

This reverts commit ce22cde218638c4e8beb9d0d153b53bc383c0918.

The commit was throwing an exception:

    java.lang.RuntimeException: javax.jms.MessageFormatException: Body not assignable to interface javax.jms.TextMessage
        at org.jboss.as.quickstarts.mdb.HelloWorldQueueMDB.onMessage(HelloWorldQueueMDB.java:56)