Warren Buffett and Greg Abel, pictured as Squishmallows here, placed a fresh bet on Delta Air Lines last quarter. Theron Mohamed/Business Insider Berkshire Hathaway tripled its Alphabet stake and placed a new bet on Delta Air Lines last quarter. The company appears to have sold all of the departed Todd Combs' stock picks. Warren Buffett's successor as CEO, Greg Abel, exited bets including Amazon, Visa, and Mastercard. Warren Buffett's successor certainly isn't shy about shaking things up . Greg Abel , who took over as Berkshire Hathaway's CEO on January 1, made sweeping changes to the conglomerate's holdings in the first three months of this year, a regulatory filing revealed on Friday. Berkshire built a fresh stake in Delta Air Lines worth $2.6 billion at the end of March, marking its return to owning airline stocks. The company also more than tripled its stake in Google-parent Alphabet, a key player in the AI boom .…