We flew the 9PM from JFK to LHR earlier this month and dinner was still served (in steerage, anyway). I would think that any meal service (sandwiches included) would still mean that the lights were kept on during the service so not much of an earlier lights out. Not that it would affect me much. To my frustration, while I can sleep pretty much anywhere I can't manage more than a restless doze on a plane.
I would expect there to be some mention of a lack of a meal on a specific flight, so that passengers could plan accordingly. On Delta's website you would get the list of what your fare class included on that flight and fare class (light snack, beverage).
I appreciate the head's up, OP, as I'll be flying JFK to LHR again next month.