Remove pawncount array in imbalance

Remove pawncount array in imbalance

This is a natural follow up to last commit where values on the
QuadraticOurs diagonal and some piece value deltas were changed.
@Stefano80 tried to simplify the newly introduced pawncount array
using QuadraticOurs[1][1] =52 and a -30 adjustment on pawn values

His STC [-3,1] was green
http://tests.stockfishchess.org/tests/view/5b707f5b0ebc5902bdba2745
but not his LTC[-3,1]
http://tests.stockfishchess.org/tests/view/5b7095700ebc5902bdba2a49

So I started a 80000 30+0.3 SPSA on the QuadraticOurs diagonal and
on the piece values using @Stefano80 start values.

SPSA gave the new values QuadraticOurs[1][1] =38 and a -33 on pawn
values (the other changes on QuadraticOurs were kept, but were not
ignificant according to this test
http://tests.stockfishchess.org/tests/view/5b710ccb0ebc5902bdba2f27)

STC
http://tests.stockfishchess.org/tests/view/5b710b220ebc5902bdba2f19
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 50902 W: 11214 L: 11150 D: 28538

LTC
http://tests.stockfishchess.org/tests/view/5b7124ef0ebc5902bdba3106
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 34271 W: 5852 L: 5753 D: 22666

Closes https://github.com/official-stockfish/Stockfish/pull/1735

bench: 4738555