Reduce full depth search twice
Passed STC:
https://tests.stockfishchess.org/tests/view/679f429e0774dfd78deb10a5
LLR: 2.95 (-2.94,2.94) <0.00,2.00>
Total: 71584 W: 18905 L: 18529 D: 34150
Ptnml(0-2): 302, 8372, 18081, 8722, 315
Passed LTC:
https://tests.stockfishchess.org/tests/view/679f72a00774dfd78deb1102
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 353952 W: 91007 L: 90024 D: 172921
Ptnml(0-2): 375, 39163, 96921, 40138, 379
closes https://github.com/official-stockfish/Stockfish/pull/5848
Bench: 3642363