Clarify context url of delta responses for containment navigation properties

Change current text: The context URL of a delta response is the same as the context URL of the root entity set, followed by /$delta. to new text: The context URL of a delta response is the context URL of the response to the defining query, followed by /$delta. If the entities are contained, then entity-set is the top-level entity set followed by the path to the containment navigation property of the containing entity.