In the brutal war for premium-class flyers, Delta Air Lines is counting on food. The carrier, looking to up its gastronomical game in first class, or Delta One, has struck an alliance with Union Square Hospitality Group, owner of Shake Shack and restaurants like Union Square Cafe, Blue Smoke and Gramercy Tavern. The beneficiary is the high-flying international-trip traveller out of Kennedy. The food is meant to be just as good as the food set on the table in Union Square’s restaurants.