Cynthia Littleton Business EditorAMC Networks hopes to mark a new beginning in the coming year as it prepares for some very big goodbyes.AMC is preparing to leverage the marketing platform provided by three buzzy series finales — AMC’s “The Walking Dead” and “Better Call Saul” and BBC America’s “Killing Eve” — to drive awareness and subscribers to its growing suite of streaming services, from drama-centric AMC Plus and SundanceNow to the niche-targeted Acorn TV, ALLBLK and Shudder.The company