[BitBoard] Remove unused genShift

BitBoard.cpp

@@ -25,10 +25,6 @@ std::ostream &operator<<(std::ostream &os, const BitBoard &board) {
     return os;
 }
 
-BitBoard BitBoard::genShift(BitBoard x, const int s) {
-    return (s < 0) ? (x >> -s) : (s > 63) ? x : (x << s);
-}
-
 BitBoard BitBoard::northFill() const {
     BitBoard result(mBoard);
     result |= (result << 8);

BitBoard.hpp

@@ -124,8 +124,6 @@ public:
 
 private:
     U64 mBoard = {};
-
-    static BitBoard genShift(BitBoard x, int s);
 };
 
 // Relational operators