Remove 'fake' ponder hit that keeps killer moves (#644)

I had some kind of fake ponder hit that relied on saving the last move.
If the new one matched with the one predicted by the engine, i'd avoid clearing the killers and send the results of the last search before starting the new one.
This adds complexity & potential bugs while apparently not gaining elo now

src/Lynx/Search/IDDFS.cs

@@ -85,7 +85,13 @@ public sealed partial class Engine
                 return onlyOneLegalMoveSearchResult;
             }
 
-            depth = CheckPonderHit(ref lastSearchResult, depth);
+            Debug.Assert(_killerMoves.Length == 3);
+            Array.Clear(_killerMoves[0]);
+            Array.Clear(_killerMoves[1]);
+            Array.Clear(_killerMoves[2]);
+            // Not clearing _quietHistory on purpose
+            // Not clearing _captureHistory on purpose
+
             if (lastSearchResult is not null)
             {
                 await _engineWriter.WriteAsync(InfoCommand.SearchResultInfo(lastSearchResult));
@@ -271,46 +277,6 @@ private bool OnlyOneLegalMove([NotNullWhen(true)] out SearchResult? result)
         return false;
     }
 
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    private int CheckPonderHit(ref SearchResult? lastSearchResult, int depth)
-    {
-        if (Game.MoveHistory.Count >= 2
-            && _previousSearchResult?.Moves.Count > 2
-            && _previousSearchResult.BestMove != default
-            && Game.MoveHistory[^2] == _previousSearchResult.Moves[0]
-            && Game.MoveHistory[^1] == _previousSearchResult.Moves[1])
-        {
-            _logger.Debug("Ponder hit");
-
-            lastSearchResult = new SearchResult(_previousSearchResult);
-
-            Array.Copy(_previousSearchResult.Moves.ToArray(), 2, _pVTable, 0, _previousSearchResult.Moves.Count - 2);
-
-            for (int d = 0; d < Configuration.EngineSettings.MaxDepth - 2; ++d)
-            {
-                _killerMoves[0][d] = _previousKillerMoves[0][d + 2];
-                _killerMoves[1][d] = _previousKillerMoves[1][d + 2];
-                _killerMoves[2][d] = _previousKillerMoves[2][d + 2];
-            }
-
-            // Re-search from depth 1
-            depth = 1;
-        }
-        else
-        {
-            Array.Clear(_killerMoves[0]);
-            Array.Clear(_killerMoves[1]);
-            Array.Clear(_killerMoves[2]);
-            Debug.Assert(_killerMoves.Length == 3);
-
-            // Not clearing _quietHistory on purpose
-
-            // Not clearing _captureHistory on purpose
-        }
-
-        return depth;
-    }
-
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     private SearchResult UpdateLastSearchResult(SearchResult? lastSearchResult,
         int bestEvaluation, int alpha, int beta, int depth, bool isMateDetected, int bestEvaluationAbs)