Simplify probCutDepth term
Passed STC
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 139392 W: 36003 L: 35897 D: 67492
Ptnml(0-2): 451, 16383, 35911, 16511, 440
https://tests.stockfishchess.org/tests/view/697ebb4d5f56030af97b5aa5
Passed LTC
LLR: 2.97 (-2.94,2.94) <-1.75,0.25>
Total: 266934 W: 67822 L: 67851 D: 131261
Ptnml(0-2): 175, 29579, 73955, 29616, 142
https://tests.stockfishchess.org/tests/view/6980e5a26362aee5c8a55398
closes https://github.com/official-stockfish/Stockfish/pull/6607
Bench: 2515956