[WFLY-3675] Remove mod_cluster ContextHost and Proxy classes and use res...

...olveModelAttribute() instead

https://issues.jboss.org/browse/WFLY-3675

Goodbye hacky classes.
The policy has always been to keep the messages in commented out so that they dont get accidentally reused. I dont see a reason for changing this policy since as Brian says, we still keep the mapping in EAP IDs to updated WF IDs.

If we have already done the renumbering, but we havent had any WF release yet, I suggest (in in separata PR) I will remove unused methods, renumber in WF and update the mapping file in EAP. Anyone see problem with that?