The Federal Deposit Insurance Corp. must face a $10 billion lawsuit over the toxic remnants of Washington Mutual Bank, a federal judge ruled. Judge Rosemary M. Collyer of the U.S. District Court in Washington, D.C., refused the FDIC’s bid to dismiss a lawsuit filed by a unit of Deutsche Bank AG over soured pools of mortgage loans made by Washington Mutual, or WaMu, a big player in the home mortgage boom before it was seized by regulators in the largest bank failure in U.S. history.