🔍 Avoid doing TT cutoffs on PV nodes

[eduherminio]

Seems kinda neutral after the second attempt.
Let's hope this helps fixing some repetition issues

Score of Lynx-experiment-no-tt-cutoffs-pvnode-2591-win-x64 vs Lynx 2589 - main: 4169 - 4366 - 5490  [0.493] 14025
...      Lynx-experiment-no-tt-cutoffs-pvnode-2591-win-x64 playing White: 2854 - 1346 - 2812  [0.608] 7012
...      Lynx-experiment-no-tt-cutoffs-pvnode-2591-win-x64 playing Black: 1315 - 3020 - 2678  [0.378] 7013
...      White vs Black: 5874 - 2661 - 5490  [0.615] 14025
Elo difference: -4.9 +/- 4.5, LOS: 1.6 %, DrawRatio: 39.1 %
SPRT: llr -2.27 (-78.6%), lbound -2.25, ubound 2.89 - H0 was accepted

Test  | experiment/no-tt-cutoffs-pvnode
Elo   | 0.73 +- 2.57 (95%)
SPRT  | 8.0+0.08s Threads=1 Hash=32MB
LLR   | 2.89 (-2.25, 2.89) [-3.00, 1.00]
Games | N: 43982 W: 13851 L: 13758 D: 16373
Penta | [1785, 5043, 8269, 5082, 1812]
https://openbench.lynx-chess.com/test/190/