Support DELETE/PUT to $ref of a collection-valued nav prop to remove/replace all links

Today you can "unlink" a resource from a single-valued nav prop using DELETE ~/EntitySet(key)/SingleNav/$ref.

With the new set operations, we could support deleting all references from a collection-valued nav prop using DELETE ~/EntitySet(key)/CollectionNav/$ref.

We should also consider supporting PUT ~/EntitySet(key)/CollectionNav/$ref with an array of keys to replace the links with those provided in the payload.

For containment, the specified links would have to already be in the collection; any links not in the collection would be removed (and, because it's containment, deleted).