Retire MovePicker::see_sign()

No more used after last patch.

No functional change.

src/movepick.cpp

@@ -179,11 +179,6 @@ void MovePicker::score<EVASIONS>() {
           m.value = history[pos.moved_piece(m)][to_sq(m)] + fromTo.get(c, m);
 }
 
-int MovePicker::see_sign() const
-{
-  return  stage == GOOD_CAPTURES ?  1
-        : stage == BAD_CAPTURES  ? -1 : 0;
-}
 
 /// next_move() is the most important method of the MovePicker class. It returns
 /// a new pseudo legal move every time it is called, until there are no more moves

src/movepick.h

@@ -104,7 +104,6 @@ public:
   MovePicker(const Position&, Move, Depth, Search::Stack*);
 
   Move next_move();
-  int see_sign() const;
 
 private:
   template<GenType> void score();