Remove very ancient tuple-counting infrastructure (IncrRetrieved() and

friends).  This code has all been ifdef'd out for many years, and doesn't
seem to have any prospect of becoming any more useful in the future.
EXPLAIN ANALYZE is what people use in practice, and I think if we did want
process-wide counters we'd be more likely to put in dtrace events for that
than try to resurrect this code.  Get rid of it so as to have one less detail
to worry about while refactoring execMain.c.