Clears the update/remove flags when you cancel.

This is a fix for #4543. When you cancel the "Remove/Update and Quit"
dialog, it was not clearing the update/remove flags. So, the next time
you use the Extension Manager it would still think that it needed to
update or remove.
Merge pull request #4700 from adobe/dangoor/4543-cancel-update

Extension Manager: Clears the update/remove flags when you cancel.