Simplify Away Negative Extension

This patch simplifies away the negative extension applied when the value returned by the transposition table is assumed to fail low over the value of reduced search.

Passed STC:
LLR: 2.99 (-2.94,2.94) <-1.75,0.25>
Total: 248736 W: 64293 L: 64302 D: 120141
Ptnml(0-2): 925, 29833, 62831, 29884, 895
https://tests.stockfishchess.org/tests/view/663bee3bca93dad645f7f64a

Passed LTC:
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 254970 W: 64289 L: 64308 D: 126373
Ptnml(0-2): 110, 28428, 70422, 28421, 104
https://tests.stockfishchess.org/tests/view/663c11f0c0b75d7f7b97d4bb

closes official-stockfish#5226

Bench: 2353057

src/search.cpp

@@ -1087,10 +1087,6 @@ Value Search::Worker::search(
                 // If we are on a cutNode but the ttMove is not assumed to fail high over current beta (~1 Elo)
                 else if (cutNode)
                     extension = -2;
-
-                // If the ttMove is assumed to fail low over the value of the reduced search (~1 Elo)
-                else if (ttValue <= value)
-                    extension = -1;
             }
 
             // Extension for capturing the previous moved piece (~0 Elo on STC, ~1 Elo on LTC)