Core: Improve ordering of boot

- Smplification of graphics backend startup/shutdown.
- Don't send complete message until CPU is ready to execute.
- Remove redundant stop message.
- Remove OSD message with backend name.

Source/Core/DolphinNoGUI/MainNoGUI.cpp

@@ -83,10 +83,9 @@ static Common::Event updateMainFrameEvent;
 void Host_Message(int Id)
 {
   if (Id == WM_USER_STOP)
-  {
     s_running.Clear();
+  if (Id == WM_USER_JOB_DISPATCH || Id == WM_USER_STOP)
     updateMainFrameEvent.Set();
-  }
 }
 
 static void* s_window_handle = nullptr;