Simplify post-lmr conthist bonus
Passed Non-regression STC:
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 49184 W: 12735 L: 12528 D: 23921
Ptnml(0-2): 134, 5746, 12647, 5909, 156
https://tests.stockfishchess.org/tests/view/6765cd2e86d5ee47d954420e
Passed Non-regression LTC:
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 177270 W: 45227 L: 45166 D: 86877
Ptnml(0-2): 132, 19498, 49302, 19583, 120
https://tests.stockfishchess.org/tests/view/676721fd86d5ee47d9544489
closes https://github.com/official-stockfish/Stockfish/pull/5734
Bench: 1042099