Remove quiet history pruning depth limit

This patch removes lmrDepth limit for quiet moves history based pruning.

Previously removal of this type of depth limits was considered bad because it
was performing bad for matetrack - but with this pruning heuristic this
shouldn't be that bad because it's "naturally" depth limited by history
threshold and should be completely disabled at depth >= 15 or so.  Also this
heuristic in previous years was known to scale non-linearly - bigger lmrDepth
thresholds were better at longer time controls and removing it completely
probably should scale pretty well.

Passed STC:
https://tests.stockfishchess.org/tests/view/6692b89b4ff211be9d4eab21
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 114464 W: 29675 L: 29545 D: 55244
Ptnml(0-2): 372, 12516, 31329, 12640, 375

Passed LTC:
https://tests.stockfishchess.org/tests/view/6692c4554ff211be9d4eab3d
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 67746 W: 17182 L: 17014 D: 33550
Ptnml(0-2): 28, 6993, 19652, 7183, 17

closes https://github.com/official-stockfish/Stockfish/pull/5485

Bench: 1250388

src/search.cpp

@@ -1022,7 +1022,7 @@ moves_loop:  // When in check, search starts here
                   + thisThread->pawnHistory[pawn_structure_index(pos)][movedPiece][move.to_sq()];
 
                 // Continuation history based pruning (~2 Elo)
-                if (lmrDepth < 6 && history < -4165 * depth)
+                if (history < -4165 * depth)
                     continue;
 
                 history += 2 * thisThread->mainHistory[us][move.from_to()];