Simplify optimism scaling formula
Passed STC non-reg:
LLR: 2.92 (-2.94,2.94) <-1.75,0.25>
Total: 110624 W: 28564 L: 28429 D: 53631
Ptnml(0-2): 169, 13076, 28801, 12983, 283
https://tests.stockfishchess.org/tests/view/6a6dd611c054e285ae029b86
Passed LTC non-reg:
LLR: 2.96 (-2.94,2.94) <-1.75,0.25>
Total: 153366 W: 39831 L: 39746 D: 73789
Ptnml(0-2): 36, 16358, 43841, 16381, 67
https://tests.stockfishchess.org/tests/view/6a6f96c82cf557d58a2e188b
closes https://github.com/official-stockfish/Stockfish/pull/7037
Bench: 2119477