gpuAccelerationOfNonbondedIsUseful() prints warning twice
The routine always prints the warning, and at least with two thread-mpi ranks the routine is called twice on master.
Fix duplicate warning
Thread-MPI, GPUs and energy groups was issuing this warning
twice. Note that no-MPI and real-MPI are still handled correctly -
they warn on the second call, which is the only one made in those