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/Frame.cpp

@@ -143,7 +143,7 @@ void CRenderFrame::OnDropFiles(wxDropFilesEvent& event)
   }
   else
   {
-    DVDInterface::ChangeDiscAsHost(filepath);
+    Core::RunAsCPUThread([&filepath] { DVDInterface::ChangeDisc(filepath); });
   }
 }