Simplify quiet history update expression
This patch simplifies the quiet history update expression in search.cpp.
The change is behaviour‑identical and removes unnecessary complexity from
the update_quiet_histories call.
Passed STC (non‑regression):
https://tests.stockfishchess.org/tests/view/6a14367b818cacc1db0ac7c3
LLR: 2.96 (-2.94,2.94) <-1.75,0.25>
Total: 52224 W: 13338 L: 13135 D: 25751
Ptnml(0-2): 118, 6065, 13557, 6240, 132
Passed LTC (non‑regression):
https://tests.stockfishchess.org/tests/view/6a155046818cacc1db0ac94d
LLR: 2.96 (-2.94,2.94) <-1.75,0.25>
Total: 136812 W: 34689 L: 34586 D: 67537
Ptnml(0-2): 51, 14770, 38668, 14859, 58
Both STC and LTC passed. Patch rebased to latest master.
closes https://github.com/official-stockfish/Stockfish/pull/6863
Bench: 2549662