Fixed a simple typo in LoadingScreenManager (#417)

In LoadingScreenManager.cs we subscribed to a listener in OnDisable instead of unsubscribing.

UOP1_Project/Assets/Scripts/SceneManagement/LoadingScreenManager.cs

 	{
 		if (_ToggleLoadingScreen != null)
 		{
-			_ToggleLoadingScreen.OnEventRaised += ToggleLoadingScreen;
+			_ToggleLoadingScreen.OnEventRaised -= ToggleLoadingScreen;
 		}
 	}