simplify see pruning in qsearch

passed non-regression STC:
LLR: 2.96 (-2.94,2.94) <-1.75,0.25>
Total: 34880 W: 9193 L: 8968 D: 16719
Ptnml(0-2): 103, 4047, 8935, 4232, 123
https://tests.stockfishchess.org/tests/view/66ee83bd86d5ee47d953b15b

passed non-regression LTC:
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 69126 W: 17529 L: 17357 D: 34240
Ptnml(0-2): 41, 7507, 19285, 7699, 31
https://tests.stockfishchess.org/tests/view/66ef3e0386d5ee47d953b1d3

closes #5607

Bench: 1339840

src/search.cpp

@@ -1596,19 +1596,11 @@ Value Search::Worker::qsearch(Position& pos, Stack* ss, Value alpha, Value beta)
                     continue;
                 }
 
-                // If static eval is much lower than alpha and move is
-                // not winning material, we can prune this move. (~2 Elo)
-                if (futilityBase <= alpha && !pos.see_ge(move, 1))
+                // if static exchange evaluation is low enough
+                // we can prune this move. (~2 Elo)
+                if (!pos.see_ge(move, alpha - futilityBase))
                 {
-                    bestValue = std::max(bestValue, futilityBase);
-                    continue;
-                }
-
-                // If static exchange evaluation is much worse than what
-                // is needed to not fall below alpha, we can prune this move.
-                if (futilityBase > alpha && !pos.see_ge(move, (alpha - futilityBase) * 4))
-                {
-                    bestValue = alpha;
+                    bestValue = (futilityBase > alpha) ? alpha : std::max(bestValue, futilityBase);
                     continue;
                 }
             }