Reduce the size of internal node tables

In !3067 (merged) the DEFAULT_NODE_LOCK_COUNT was bumped from 7 to 53 that affects number of internal structures allocated (node locks, deadlists, rdatasets, heaps) supposedly to reduce contention in the rbtdb, but at the same time it would increase a per-zone memory consumption.

With better testing that we have available now, it was shown that the effect of increasing the count is negligible and it's not worth the memory increase that could be as much as double when many zones or many records are loaded into named.