[wsia][wsrp-interfaces] expires in EntityContext

[Rich Thompson <richt2@us.ibm.com>]

Considering that we decided at the face-to-face that all entities are
presistent, what would this expires refer to? I think it came in as
treating the state pushed to the Consumer in the same manner as the pushed
state in RequestContext. However, I think the persistent nature of Entity
state makes this meaningless.