In what would be the largest merger of the year, Dallas-based AT&T has agreed to acquire New York-based Time Warner in an $85.4 billion deal. The boards of both companies unanimously approved the acquisition today. “Premium content always wins,” AT&T CEO Randall L. Stephenson, said in a statement. “We’ll have the world’s best premium content with the networks to deliver it to every screen.” Stephenson will lead the combined company while while Time Warner CEO Jeff Bewkes will depart…