removed second killer move

STC with movepicker rewrite:

LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 46656 W: 12208 L: 11995 D: 22453
Ptnml(0-2): 203, 5461, 11777, 5694, 193
https://tests.stockfishchess.org/tests/view/668d98a15034141ae5999e68

Earlier version passed STC:
LLR: 2.94 (-2.94,2.94) <0.00,2.00>
Total: 468896 W: 120999 L: 120054 D: 227843
Ptnml(0-2): 1207, 55209, 120639, 56218, 1175
https://tests.stockfishchess.org/tests/view/668b17d2cf91c430fca58630

Earlier version passed LTC:
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 550524 W: 139553 L: 139877 D: 271094
Ptnml(0-2): 333, 61646, 151616, 61346, 321
https://tests.stockfishchess.org/tests/view/668b2e04cf91c430fca586b1

closes https://github.com/official-stockfish/Stockfish/pull/5472

bench 1234309

Co-authored-by: rn5f107s2 <clemens.lerchl@gmail.com>

src/movepick.h

@@ -160,7 +160,7 @@ class MovePicker {
                const CapturePieceToHistory*,
                const PieceToHistory**,
                const PawnHistory*,
-               const Move*);
+               Move);
     MovePicker(const Position&,
                Move,
                Depth,
@@ -185,7 +185,7 @@ class MovePicker {
     const PieceToHistory**       continuationHistory;
     const PawnHistory*           pawnHistory;
     Move                         ttMove;
-    ExtMove refutations[2], *cur, *endMoves, *endBadCaptures, *beginBadQuiets, *endBadQuiets;
+    ExtMove killer, *cur, *endMoves, *endBadCaptures, *beginBadQuiets, *endBadQuiets;
     int     stage;
     int     threshold;
     Depth   depth;