Brian Steinberg Senior TV EditorJoanne LaMarca, the spirited executive producer behind the fourth hour of NBC’s “Today” morning franchise, plans to step down from the role later in August.In a memo issued to staffers on Thursday, Libby Leist, a senior vice president at NBC News who oversees “Today,” said LaMarca was eager to spend more time with family, and had initially taken the job in 2019 with the intention to stay for a year.