Fix dev warning. (#980)

src/ftxui/dom/selection.cpp

@@ -15,7 +15,7 @@ class Unselectable : public NodeDecorator {
  public:
   using NodeDecorator::NodeDecorator;
 
-  void Select(Selection& selection) override {
+  void Select(Selection&) override {
     // Overwrite the select method to do nothing.
   }
 };

src/ftxui/dom/selection_style.cpp

@@ -20,7 +20,7 @@ class SelectionStyleReset : public NodeDecorator {
 
   void Render(Screen& screen) final {
     auto old_style = screen.GetSelectionStyle();
-    screen.SetSelectionStyle([](Pixel& pixel) {});
+    screen.SetSelectionStyle([](Pixel&) {});
     NodeDecorator::Render(screen);
     screen.SetSelectionStyle(old_style);
   }

src/ftxui/dom/text.cpp

@@ -88,7 +88,6 @@ class Text : public Node {
   bool has_selection = false;
   int selection_start_ = 0;
   int selection_end_ = -1;
-  std::function<void(Pixel& pixel)> selectionTransform;
 };
 
 class VText : public Node {