Retire quietsSearched[]

Use MovePicker moves[] to access already tried
quiet moves. A bit of care shall be taken
to avoid calling stage_moves() when we are still
at ttMove stage, because moves are yet to be
generated. Actually our staging move generation
makes this code a bit more tricky than what I'd
like, but removing an ausiliary redundant
array like quietsSearched[] is a good thing.

Idea by DiscoCheck

bench: 9355734

src/movepick.h

@@ -88,6 +88,7 @@ public:
   MovePicker(const Position&, Move, const HistoryStats&, PieceType);
   MovePicker(const Position&, Move, Depth, const HistoryStats&, Move*, Search::Stack*);
 
+  const ExtMove* stage_moves() const;
   template<bool SpNode> Move next_move();
 
 private: