Simplify bestvalue formula
Passed STC:
LLR: 2.97 (-2.94,2.94) <-1.75,0.25>
Total: 163680 W: 42689 L: 42605 D: 78386
Ptnml(0-2): 619, 19555, 41386, 19683, 597
https://tests.stockfishchess.org/tests/view/66f9451386d5ee47d953b7d9
Passed LTC:
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 96498 W: 24582 L: 24438 D: 47478
Ptnml(0-2): 62, 10642, 26718, 10744, 83
https://tests.stockfishchess.org/tests/view/66fd765786d5ee47d953ba1c
closes https://github.com/official-stockfish/Stockfish/pull/5622
Bench: 1309815