nbody: eliminate 'N % g_numCPUCores' check

This causes the app to not function if the system's CPU count is not a power of
two. I have a 24-thread Westmere box which it decided to not function on.

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
nbody: clean up printout format if/when user hits a hotkey

Signed-off-by: Steven Noonan <steven@uplinklabs.net>