Veteran “60 Minutes” producer Michael Gavshon, who produced a piece for Anderson Cooper that came under heavy scrutiny from CBS News boss Bari Weiss, has resigned from the network, sources said. Gavshon wrote in a memo obtained by The Post that his decades-long career at CBS News will come to an end on June 30 — after a slew of high-profile journos were recently axed from the newsmagazine. “Thirty-four of my forty-one years at CBS News have been at ’60 Minutes,'” wrote Gavshon, who was based in