The announcement reverses a decision last week, when Twitter said Mr. Musk would become a board member after amassing a 9.2 percent stake in the company. Elon Musk, the world’s wealthiest man and the biggest shareholder of Twitter, will no longer join the social media service’s board of directors, the company said late Sunday. The move capped a whirlwind week at Twitter that had been set off by Mr. Musk, 50. On Tuesday, Twitter announced that the billionaire would be appointe