[$] Removing the scheduler's energy-margin heuristic

The CPU scheduler's job has never been easy; it must find a way to allocateCPU time to all tasks in the system that is fair, allows all tasks toprogress, and maximizes the throughput of the system as a whole. Morerecently, it has been called upon to satisfy another constraint: minimizingthe system's energy consumption. There is currently apatch set in circulation, posted by Vincent Donnefort with work fromDietmar Eggemann as well, that changes how this constraint is met. Theactual change is small, but it illustrates how hard it can be to get theneeded heuristics right.