DolphinQt: Remove the "supported Bluetooth device could not be found" label from ControllersPane.

It just confuses DolphinBar users and isn't relevant these days now that Windows users do not use alternative Bluetooth stacks.

Source/Core/DolphinQt/Config/ControllersPane.h

@@ -13,9 +13,6 @@ class ControllersPane final : public QWidget
 public:
   ControllersPane();
 
-protected:
-  void showEvent(QShowEvent* event) override;
-
 private:
   void CreateMainLayout();