LONDON — Amazon. com was marketing a collection of President Xi Jinping’s speeches and writings on its Chinese website about two years ago, when Beijing issued an edict, according to two other people familiar with the incident. to prevent visitor ratings and reviews from being allowed in China. A negative review of Xi’s e-book sparked demand, one of the other people said. “I think the challenge has less than five stars,” the highest score of Amazon’s five-point system, the other user said. Ratings and reviews are a component of Amazon’s e-commerce business, a primary way to have interactive shoppers. But…