Tweak formula for pruning moves losing material

Tweak formula for pruning moves losing material

Simplify the "Prune moves with negative SEE" formula,
by removing one multiplication and subtraction operation.

Passed STC:
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 214272 W: 54596 L: 54572 D: 105104
Ptnml(0-2): 741, 25160, 55320, 25164, 751
https://tests.stockfishchess.org/tests/view/64c430d1dc56e1650abbdbf6

Passed LTC:
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 238380 W: 60600 L: 60601 D: 117179
Ptnml(0-2): 132, 26069, 66791, 26064, 134
https://tests.stockfishchess.org/tests/view/64c81f155b17f7c21c0cee2b

closes https://github.com/official-stockfish/Stockfish/pull/4721

bench: 1655337