Plans to convert New York’s Seventh Regiment Armory into an upscale performance venue hit a snag this week, when Lincoln Center canceled its plans for a production of Tristan und Isolde because of the high cost of preparing the space. “The armory and Drill Hall, its 55,000-square-foot, column-free space, has long been eyed hungrily by performing arts presenters,” and the overall plan to renovate the armory shouldn’t be derailed by the cancellation.