Remove DVDInterface::ChangeDiscAsHost

There isn't much point in keeping this utility function around
now that RunAsCPUThread provides a simple way of running things
on the CPU thread.

Source/Core/DolphinWX/FrameTools.cpp

@@ -369,7 +369,7 @@ void CFrame::DoOpen(bool Boot)
   }
   else
   {
-    DVDInterface::ChangeDiscAsHost(WxStrToStr(path));
+    Core::RunAsCPUThread([&path] { DVDInterface::ChangeDisc(WxStrToStr(path)); });
   }
 }