Qt/GeneralWidget and GraphicsWidget: Remove unused member variable

m_xrr_config was used by the GeneralWidget::GetAvailableResolutions
function to get the list of supported fullscreen resolutions when
HAVE_XRANDR was set. aa4088a removed the ability to set that resolution
in the UI, leaving the GetAvailableResolutions function unused.

m_xrr_config is initialized in MainWindow which still uses it to toggle
fullscreen, but the references in GeneralWidget and GraphicsWidget
(which just ferried m_xrr_config from MainWindow to GeneralWidget) are
now unnecessary and removed in this commit.

Source/Core/DolphinQt/Config/Graphics/GeneralWidget.h

@@ -16,16 +16,11 @@ class QRadioButton;
 class QGridLayout;
 class ToolTipComboBox;
 
-namespace X11Utils
-{
-class XRRConfiguration;
-}
-
 class GeneralWidget final : public GraphicsWidget
 {
   Q_OBJECT
 public:
-  explicit GeneralWidget(X11Utils::XRRConfiguration* xrr_config, GraphicsWindow* parent);
+  explicit GeneralWidget(GraphicsWindow* parent);
 signals:
   void BackendChanged(const QString& backend);
 
@@ -55,6 +50,4 @@ private:
   ConfigBool* m_render_main_window;
   std::array<GraphicsRadioInt*, 4> m_shader_compilation_mode{};
   ConfigBool* m_wait_for_shaders;
-
-  X11Utils::XRRConfiguration* m_xrr_config;
 };