remove redundant assignment of isDestroyed
[FEATURE ember-testing-triggerEvent-helper]

Adds `triggerEvent` testing helper to allow triggering of arbitrary
events on an element.
Merge pull request #3792 from rjackson/trigger_test_helper

[FEATURE ember-testing-triggerEvent-helper]
Merge pull request #3480 from Lowest0ne/remove-redundant-assignment

remove redundant assignment of isDestroyed