Toggle function in docs even though it's removed

[ghost]

In the section regarding event helpers (https://github.com/jquery/learn.jquery.com/page/events/event-helpers.md)
toggle() has been deprecated since 1.8 and removed since 1.9 (now toggle() is used to make an element not visible)

[scottgonzalez]

@ajpiano I just added a note on this page rather than removing the section. I figure there are enough people using older versions that it might still be relevant, though we really don't want to encourage developers to use methods that don't exist in newer versions. If we remove the section, then this page will only have one method to talk about. Let me know what you think we should do.