May 15 (Reuters) – 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 in Amazon.com and UnitedHealth Group. The changes are part of a portfolio reshuffling that followed the recent departure of an investment manager who helped Berkshire Chairman Warren Buffett invest the conglomerate’s cash. According to a reg…