retire divide command

This command is redundant with perft. Or, rather, it is what perft should always have been. The main purpose of perft is to be a debugging tool, so if we can't see the sum of perft(N-1), it's completely useless.

Note that the usual `2>/dev/null` can be used to trash the unwanted display and do perft speed measurements (when indulging in micro-optimizations).

No functional change.