Have fun with union in book.cpp

Fancy way to use an union to map polyglot
zobrist keys in one go.

Also some renaming while there.

No functional change.
Revert so called "fromNull patch"

Revert patch c581b7ea3627482

Seems a regression after testing from Gary:
ELO: 7.24 +- 99%: 17.03 95%: 12.93
LOS: 97.86%
Wins: 439 Losses: 381 Draws: 1962

And mine:
After 5410 games at 15"+0.05
Wins: 936 Losses: 1141 Draws: 3333  ELO -13

Moreover we know that there is a regression in the range
of patches which include the fromNull patch.

Probably this is not the only regression since 2.3.1 and
perhaps the idea under fromNull is good, but at the moment,
while in deep regression hunting, better to be on the safe
side and revert it entirely.

My guess on why this is a regression is that using the
negated evaluation of previous ply in case of null search
fails to take in account the king safety asymmetry between
the two colors. This is of course just a guess.

bench 5503830