Simplify the extension formula
Simplify the extension formula in the case of cutNode by removing the depth condition and always setting extension to -2.
Passed STC:
LLR: 2.97 (-2.94,2.94) <-1.75,0.25>
Total: 277280 W: 70760 L: 70802 D: 135718
Ptnml(0-2): 971, 31775, 73153, 31807, 934
https://tests.stockfishchess.org/tests/view/65ad08f779aa8af82b979dd6
Passed LTC:
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 452976 W: 112992 L: 113215 D: 226769
Ptnml(0-2): 266, 51041, 124112, 50788, 281
https://tests.stockfishchess.org/tests/view/65ae466fc865510db026a760
closes https://github.com/official-stockfish/Stockfish/pull/5021
Bench: 1492957