Three major brands have halted their advertising on Amazon.com Inc.’s Twitch online service, according to people with knowledge of the matter, after a controversial group of livestreamers alleged that the company is promoting antisemitic content.AT&T Inc., JPMorgan Chase & Co. and Dunkin’ Brands have all pulled spots from the gamer-oriented service, according to the people, who asked not to be identified discussing nonpublic information. A fourth sponsor, Chevron Corp., is considering ending fut...