kill smpi_process_count(), use smpi_get_universe_size() instead

kill smpi_process_count(), use smpi_get_universe_size() instead

process_count was probably the original name while universe_size was
added to implement MPI_Attr_get(MPI_UNIVERSE_SIZE). Merge both to sort
things out.

While I'm at it, move all of it to smpi_deployment to reduce the
amount of globals made visible to more than one module.