Host: Remove unnecessary function

Remove Host_UpdateMainFrame(). The only non-empty call happened in
DolphinNoGUI which called s_update_main_frame_event.Set(), but
DolphinNoGUI never waits on that event.

Source/DSPTool/StubHost.cpp

@@ -50,9 +50,6 @@ void Host_JitCacheInvalidation()
 void Host_JitProfileDataWiped()
 {
 }
-void Host_UpdateMainFrame()
-{
-}
 void Host_RequestRenderWindowSize(int, int)
 {
 }