[Cleanup] WX: Remove usage of NANDContentManager

Also clean up the way the system menu label is updated. We don't want
to access the NAND while emulation is running, and especially not
that many times per second on an unpredictable timing.

Source/Core/DolphinWX/MainMenuBar.h

@@ -42,6 +42,7 @@ private:
   wxMenu* CreateHelpMenu() const;
 
   void OnPopulatePerspectivesMenu(PopulatePerspectivesEvent&);
+  void OnUpdateWiiMenuTool(wxCommandEvent&);
 
   void RefreshMenuLabels() const;
   void RefreshPlayMenuLabel() const;