message: Remove unused textColor and selectColor
  In the case of `selectColor` the name wasn't even accurate, since it was
  actually setting the mouse hover highlight color.
diff: @@ -39,9 +39,6 @@ public:
  ListBox();
  ~ListBox() override;
  - void textColor(const NAS2D::Color& color) { mText = color; }
  - void selectColor(const NAS2D::Color& color) { mHighlightBg = color; }
  -
  void addItem(const std::string& item, int tag = 0);
  void removeItem(const std::string& item);
  bool itemExists(const std::string& item);
  