AT&T, the wireless carrier that thundered its way into the media business three years ago with grand visions of streaming video on millions of its customers’ cellphones, wants a do-over: It has agreed to spin off its WarnerMedia group and merge it with a rival programmer, Discovery Inc., the companies announced Monday.The transaction will combine HBO, Warner Bros. studios, CNN and several other cable networks with a host of reality-based cable channels from Discovery, including Oprah Winfrey’s OWN, HGTV, The Food Network and Animal Planet.The new company will join together two of the largest media businesses …
