The telecom giant will sell its 70% stake in DIRECTV, marking the end of a painful and costly era.With the sale of its 70% stake in satellite television provider DIRECTV, telecom giant AT&T (T 0.59%) is finally fully out of the media business.The company wasted many billions of dollars over the past decade in an ill-fated attempt to transform itself into a media conglomerate. It paid a staggering $48.5 billion in 2015 to acquire DIRECTV only to see subscribers jump ship. It followed up that deal a few years ...