Cynthia Littleton Business EditorThis is the winter of discontent for Hollywood workers, as no level of seniority has been spared from the wave of mass layoffs.Warner Bros. has been shaken by two rounds of layoffs and a wholesale restructuring that have ushered out veterans with decades of service to the Hollywood studio.NBCUniversal has rewired the structure of its TV content production and distribution operations, leading to hundreds of job cuts.