Going There,” which isn’t out until October but was obtained by The Post.In her sensational tell-all about her decades in cutthroat TV news, Couric, 64, admitted that competition between them was at one point careening out of control.“I loved that I was getting under Diane’s skin,” she writes, although she freely admits that Sawyer got under hers just as much.Couric spared nothing while discussing all her former co-stars including Matt Lauer and Deborah Norville, alongside the producers that