remove the "prefetch LOD levels" feature
remove the "prefetch LOD levels" feature

Not clear that it provides a large improvement from just caching indices
and the root genome, and it was slowing down first accesses in
high-latency situations.

glennhickey/hal,glennhickey/hal,glennhickey/hal,glennhickey/hal,glennhickey/hal,glennhickey/hal,glennhickey/hal,glennhickey/hal