Remove bonus for killers.

Passed non-regression STC:
LLR: 2.94 (-2.94,2.94) {-1.25,0.25}
Total: 14712 W: 1416 L: 1315 D: 11981
Ptnml(0-2): 59, 1029, 5082, 1124, 62
https://tests.stockfishchess.org/tests/view/5fbfa31f67cbf42301d6b36e

Passed non-regression LTC:
LLR: 2.95 (-2.94,2.94) {-0.75,0.25}
Total: 27536 W: 1099 L: 1044 D: 25393
Ptnml(0-2): 11, 929, 11838, 974, 16
https://tests.stockfishchess.org/tests/view/5fbfac9167cbf42301d6b371

closes https://github.com/official-stockfish/Stockfish/pull/3241

Bench: 3887644