refactor: change demo window declaration

include/render/gui/FrameMenu.h

@@ -9,6 +9,7 @@ class FrameMenu : public GuiWidget {
 private:
     bool m_VSync;
     bool m_IsometricView;
+    bool m_ShowDemoWindow;
 public:
     FrameMenu(client::Client* client);
 

include/render/gui/TowerGui.h

@@ -43,8 +43,6 @@ private:
     std::unique_ptr<td::gui::GameMenu> m_GameMenu;
     std::unique_ptr<td::gui::FrameMenu> m_FrameMenu;
     std::unique_ptr<td::gui::UpdateMenu> m_UpdateMenu;
-
-    bool m_DemoOpened = true;
 public:
     TowerGui(SDL_Window* wndow, SDL_GLContext glContext, td::render::Renderer* renderer);
     ~TowerGui();