Simplify move generation (2/2)

Simplify move generation (2/2)

STC:
LLR: 2.97 (-2.94,2.94) {-1.25,0.25}
Total: 39352 W: 3551 L: 3493 D: 32308
Ptnml(0-2): 143, 2695, 13928, 2781, 129
https://tests.stockfishchess.org/tests/view/6050007a2433018de7a38bbb

LTC:
LLR: 2.96 (-2.94,2.94) {-0.75,0.25}
Total: 44944 W: 1629 L: 1596 D: 41719
Ptnml(0-2): 22, 1319, 19762, 1342, 27
https://tests.stockfishchess.org/tests/view/60500e892433018de7a38bc4

Closes https://github.com/official-stockfish/Stockfish/pull/3399

No functional change