“Some dresses were never destined for auctions or museums,” her former royal butler said.Princess Diana in Washington, D.C.Credit: GettyThe GistPrincess Diana’s wardrobe was iconic—and, according to her former royal butler Paul Burrell, she sold some of her pieces to thrift shops.The reason she did so is surprising and has ties to her sons, Prince William and Prince Harry.“Some dresses were never destined for auctions or museums,” Burrell wrote …