Add Element.Delegation test for removing an submit event in IE.

This makes Element.Delegation throw an error if the form the submit
event is added to is removed.
Fixes #2645 - Don't call removeEvent if the element is destroyed.

A destroyed element in IE8 doesn't have the removeEvent method anymore.
Neither has it the event anymore. Therefore we should skip calling
removeEvent on those form elements.
Merge pull request #2646 from arian/fix-2645-form-submit-delegation

Fix 2645 form submit delegation