Elon Musk has sent a third letter to Twitter attempting to terminate his $44 billion acquisition of the company. Musk’s legal team cited Twitter’s multimillion dollar severance payment to former security chief and whistleblower Peiter Zatko as a violation of the merger agreement and a reason to end the deal. The letter, dated September 9th, was sent to Twitter’s chief legal officer Vijaya Gadde, and was included in a filing Twitter made with the SEC on Friday (which you can read at…