Make Qt shortcuts actually work in fullscreen

Also removes hacks related to fullscreen.

src/qt/qt_mainwindow.hpp

@@ -31,7 +31,6 @@ public:
     void  blitToWidget(int x, int y, int w, int h, int monitor_index);
     QSize getRenderWidgetSize();
     void  setSendKeyboardInput(bool enabled);
-    void  checkFullscreenHotkey();
     void  reloadAllRenderers();
 
     std::array<std::unique_ptr<RendererStack>, 8> renderers;