Simplify continuation histories
Functional simplification.
Simplify continuation histories, therefore increasing the effect of
stats updates and movepicker bonuses for continuation history 3 plies
deep.
Passed STC:
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 229184 W: 59087 L: 59080 D: 111017
Ptnml(0-2): 554, 27248, 59002, 27213, 575
https://tests.stockfishchess.org/tests/view/665c7a09fd45fb0f907c223b
Passed LTC:
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 44532 W: 11419 L: 11223 D: 21890
Ptnml(0-2): 18, 4787, 12457, 4989, 15
https://tests.stockfishchess.org/tests/view/665c8842fd45fb0f907c23ec
closes https://github.com/official-stockfish/Stockfish/pull/5339
Bench: 1326444