Simplify the processing of ejb timer timeout method params

ejb timer timeout methods can take no arg, or one argument of type Timer.

Current WildFly ejb timer service impl processes timeout method params in a general way, assuming they can be any number of params of any types. We can simplify it knowing that the params can only be null / no-arg, or Timer.

Various places can be simplified, such as org.jboss.as.ejb3.timerservice.persistence.TimeoutMethod, serializing it before persisting it, deserialize it after retrieving from persistence.

In database, the column name for this is timeout_method_descriptor, and its value (varchar) may be
javax.ejb.Timer if it is a one-arg params.

Note: need to maintain backward compatibility with previous jboss_ejb_timer table schema, and legacy file data store.