“Stranger Things” star David Harbour underwent intermittent fasting and Pilates to shed dozens and dozens of pounds over just eight months so he could convincingly play the Sheriff Jim Hopper in the recently released fourth season. “I lost about 80 pounds from season three — I was about 270 [then], and when we shot [season four] I was around 190,” the White Plains native, 47, told British GQ in a new interview. But it was a one and done experience for the actor. “I don’t think I’ll ever do that again,” said Harbour, noting he regained the weight while working on an upcoming Santa Claus flick. …