Simplify away capthist bonus in Probcut
The explicit bonus has been obsoleted with the introduction of #5695
Passed Non-regression STC:
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 132832 W: 34519 L: 34403 D: 63910
Ptnml(0-2): 430, 15754, 33931, 15872, 429
https://tests.stockfishchess.org/tests/view/678158c49168c8bf30927834
Passed Non-regression LTC:
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 123492 W: 31426 L: 31309 D: 60757
Ptnml(0-2): 79, 13705, 34051, 13842, 69
https://tests.stockfishchess.org/tests/view/6782b07e6ddf09c0b4b6dbb7
closes https://github.com/official-stockfish/Stockfish/pull/5761
Bench: 1180439