Remove some conditions at PV improvement reduction

Remove some conditions at PV improvement reduction

Non-regression STC:
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 63664 W: 17007 L: 16823 D: 29834
Ptnml(0-2): 163, 6998, 17336, 7162, 173
https://tests.stockfishchess.org/tests/view/6430b124028b029b01ac99f2

Non-regression LTC:
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 90016 W: 24399 L: 24258 D: 41359
Ptnml(0-2): 52, 8672, 27405, 8841, 38
https://tests.stockfishchess.org/tests/view/64310e74028b029b01ad3131

closes https://github.com/official-stockfish/Stockfish/pull/4526

Bench: 3661938