Simplify singularDepth from the bonus formula
Passed STC non-reg:
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 124000 W: 31413 L: 31294 D: 61293
Ptnml(0-2): 139, 14508, 32614, 14573, 166
https://tests.stockfishchess.org/tests/view/6aad39bddbd128aac8fd5609
Passed LTC non-reg:
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 193296 W: 49385 L: 49341 D: 94570
Ptnml(0-2): 40, 20611, 55302, 20655, 40
https://tests.stockfishchess.org/tests/view/6ab136585146babbc9b2b54b
closes https://github.com/official-stockfish/Stockfish/pull/7191
Bench: 1714434