The latest installment of the Netflix chronicle of the royals seeks to slime Margaret Thatcher, but the Charles-Diana soap opera undermines the series’ political slant.Since its debut in 2016, fans of the Netflix series “The Crown” have been looking forward to when this depiction of the life of Queen Elizabeth II would take the story of the royal family and British politics into the 1980s. For Americans who love the show because it satisfies their yen for celebrity gossip with a gloss of politics and social commentary, the arrival of Princess Diana as a major character was highly anticipated.Much of...