Do not support expressions on the management-interface=http-interface 'http-upgrade' attribute

Our intent is to shift configuration of JBoss Remoting based management via HTTP Upgrade to use a child resource. This is needed as we want to implement this as a capability and we only want resource to provide capabilities, not attributes. Also, I suspect it will turn out to be a better API as a resource anyway, as a resource can support more than just the "off/on" behavior of the current attribute.

Allowing expressions for this attribute will make this transition much harder. I would prefer to never allow an expression for this attribute in EAP, as that will avoid any EAP compatibility problems when we move to a resource.

Changing this, however, will be a breaking API change vs WF 8/9.

I expect using an expression for this attribute will have been quite unusual.