simplified and increased threshold to switch between NNUE and classical

simplified and increased threshold to switch between NNUE and classical

STC https://tests.stockfishchess.org/tests/view/5f2deb1661e3b6af6488200f
LLR: 2.96 (-2.94,2.94) {-1.50,0.50}
Total: 10376 W: 1481 L: 1359 D: 7536
Ptnml(0-2): 91, 953, 2981, 1069, 94

LTC: https://tests.stockfishchess.org/html/live_elo.html?5f2e0a0461e3b6af64882019
LLR: 2.99 (-2.94,2.94) {-1.50,0.50}
Total: 5040 W: 375 L: 315 D: 4350
Ptnml(0-2): 7, 263, 1926, 311, 13

closes https://github.com/official-stockfish/Stockfish/pull/2934

Bench: 4067325