Remove redundant PvNode condition

After commit 6d58bf7 we always call PvNodes
with cutNode set to false.

No functional change.

src/search.cpp

@@ -549,6 +549,7 @@ namespace {
     assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
     assert(PvNode || (alpha == beta - 1));
     assert(DEPTH_ZERO < depth && depth < DEPTH_MAX);
+    assert(!(PvNode && cutNode));
 
     Move pv[MAX_PLY+1], quietsSearched[64];
     StateInfo st;
@@ -963,7 +964,7 @@ namespace {
                      +    (fmh2 ? (*fmh2)[moved_piece][to_sq(move)] : VALUE_ZERO);
 
           // Increase reduction for cut nodes
-          if (!PvNode && cutNode)
+          if (cutNode)
               r += 2 * ONE_PLY;
 
           // Decrease reduction for moves that escape a capture. Filter out