Simplify cutnode depth condition

With this patch, the depth condition for the cutnodes reduction is loosened from
tte->depth() >= depth + 3 to just tte->depth() >= depth.

Passed STC:
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 101152 W: 25830 L: 25682 D: 49640
Ptnml(0-2): 312, 11788, 26258, 11876, 342
https://tests.stockfishchess.org/tests/view/64fd15635dab775b5359eaa6

Passed LTC:
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 82542 W: 20980 L: 20824 D: 40738
Ptnml(0-2): 42, 8795, 23440, 8953, 41
https://tests.stockfishchess.org/tests/view/64fda3545dab775b5359fbf1

closes https://github.com/official-stockfish/Stockfish/pull/4780

Bench: 1479029