BUG: InteractorEventRecorder bug results warning about passive observer.

The InteractorEventRecorder watches key press events using a passive
observer. A delete event was also added as a passive observer but
the delete event caused removing an observer which resulted in the
warning.
The warning was:
vtkObject.cxx:533 Passive observer should not call AddObserver or RemoveObserver in callback.
for
vtkInteractionWidgetsPython-TestSphereWidget
and maybe other tests.