Remove MainThread_Start/Stop to increase visibility

Windows/MainWindow.cpp

@@ -1070,7 +1070,7 @@ namespace MainWindow {
 			g_InputManager.Shutdown();
 			WindowsRawInput::Shutdown();
 
-			MainThread_Stop();
+			UpdateUIState(UISTATE_EXIT);
 			KillTimer(hWnd, TIMER_CURSORUPDATE);
 			KillTimer(hWnd, TIMER_CURSORMOVEUPDATE);
 			// Main window is gone, this tells the message loop to exit.