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/Core/DolphinTool/ToolHeadlessPlatform.cpp

@@ -73,10 +73,6 @@ void Host_JitProfileDataWiped()
 {
 }
 
-void Host_UpdateMainFrame()
-{
-}
-
 void Host_RequestRenderWindowSize(int width, int height)
 {
 }