Simplify Board::create_move()
Simplify Board::create_move()

Since the demise of the Human Player class, human-typed moves are
no longer accepted, so there is less need for detailed error messages.

MarkZH/Genetic_Chess,MarkZH/Genetic_Chess,MarkZH/Genetic_Chess,MarkZH/Genetic_Chess,MarkZH/Genetic_Chess