More than 770 writers and showrunners have signed a statement saying that they will fire their agents if the WGA fails to reach an agreement with the Association of Talent Agents for a new franchise agreement. Signers include Greg Berlanti, Alfonso Cuaron, James L. Brooks, Olive Stone, John Wells, John Singleton, Aaron Sorkin, Norman Lear, Shonda Rhimes, Seth MacFarlane, Mike Schur, Tina Fey, Joss Whedon, Kenya Barris, Peter Farrelly, Matthew Weiner, Noah Hawley, David…