United sold the NYC-LON route authority to Delta.
United still kept the LHR slot, which they then leased (I think for 3 years) to Air Canada. Thus they can resume use of the slot from another city in the future as business dictates.
Delta can not fly to LHR due to the Bermuda 2 agreement, so they'll fly to LGW. Delta has a good market share in New York (after American) and should do well with the route.
United is consolidating their East Coast - Europe to IAD (Washington Dulles) where they are the dominant carrier.
Most of United's latest expansion has been focused toward Asia lately.