A little over a year after the flame of Les Sablons’ kitchen brought the historic 1912 Conductor’s Building “to life,” the upscale French restaurant cooled off its stove tops for the last time Thursday. A message on Les Sablons’ website gave no reason for the restaurant’s closure, instead thanking its staff and patrons. “We look forward to seeing all your familiar faces at our sister restaurants throughout New England,” the statement reads.