Berkshire Hathaway  on Friday disclosed a new $2.65 billion investment in Delta Air Lines and a small stake in Macy’s, and said it sold many of its smaller stock holdings including Amazon, UnitedHealth Group and the credit card networks Visa and Mastercard. The changes were part of a portfolio reshuffling in the first quarter, which followed the promotion of Greg Abel to succeed Warren Buffett as Berkshire’s chief executive. Berkshire said in a regulatory filing that it also more than tripled