Remove set statScore to zero

Simplification. Removes setting statScore to zero if negative.

STC:
LLR: 2.95 (-2.94,2.94) {-1.50,0.50}
Total: 84820 W: 16100 L: 16033 D: 52687
Ptnml(0-2): 1442, 9865, 19723, 9944, 1436
https://tests.stockfishchess.org/tests/view/5e654fdae42a5c3b3ca2e2f8

LTC:
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 57658 W: 7435 L: 7391 D: 42832
Ptnml(0-2): 441, 5397, 17104, 5451, 436
https://tests.stockfishchess.org/tests/view/5e657ce9e42a5c3b3ca2e307

closes https://github.com/official-stockfish/Stockfish/pull/2578

Bench: 5168890

src/search.cpp

@@ -1175,13 +1175,6 @@ moves_loop: // When in check, search starts from here
                              + (*contHist[3])[movedPiece][to_sq(move)]
                              - 4926;
 
-              // Reset statScore to zero if negative and most stats shows >= 0
-              if (    ss->statScore < 0
-                  && (*contHist[0])[movedPiece][to_sq(move)] >= 0
-                  && (*contHist[1])[movedPiece][to_sq(move)] >= 0
-                  && thisThread->mainHistory[us][from_to(move)] >= 0)
-                  ss->statScore = 0;
-
               // Decrease/increase reduction by comparing opponent's stat score (~10 Elo)
               if (ss->statScore >= -102 && (ss-1)->statScore < -114)
                   r--;