Disable OMP parallelization in Simulator

Created by: aroffringa

Now that the threadpool is used, it turns out there was an extra #pragma omp parallel for in the Simulator. Since this used to be a nested omp loop, it had no effect, but now that the threadpool takes care of the parallelization, omp does parallelize this loop and starts a new group of threads in each threaad, giving rise to 48^2 threads on my 48 core machine.