Remove Reduce Depth

Remove Reduce Depth at PV nodes.

STC:
LLR: 2.94 (-2.94,2.94) {-1.25,0.25}
Total: 56760 W: 6299 L: 6236 D: 44225
Ptnml(0-2): 286, 4843, 18076, 4872, 303
https://tests.stockfishchess.org/tests/view/5f41356087a5c3c63d8f53c9

LTC:
LLR: 2.95 (-2.94,2.94) {-0.75,0.25}
Total: 17496 W: 954 L: 865 D: 15677
Ptnml(0-2): 13, 768, 7098, 855, 14
https://tests.stockfishchess.org/tests/view/5f41bb7687a5c3c63d8f53f9

closes https://github.com/official-stockfish/Stockfish/pull/3055

Bench: 3555051