Simplify the recently introduced ply-based cmh bonus factor.
Replace it with a constant which is an approximation of the limit of the factor.
STC:
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 120064 W: 30967 L: 30836 D: 58261
Ptnml(0-2): 421, 14238, 30608, 14319, 446
https://tests.stockfishchess.org/tests/view/6649d146b8fa20e74c39f4ad
LTC:
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 53856 W: 13719 L: 13530 D: 26607
Ptnml(0-2): 31, 5879, 14922, 6062, 34
https://tests.stockfishchess.org/tests/view/664a027fae57c1758ac5b4ee
closes https://github.com/official-stockfish/Stockfish/pull/5270
Bench: 1355618