BUG: Fix bug #14378, ensure observer is removed in dtor

The one shot timer could still be fired after the interactor style
was removed.

Change-Id: I7425293ecf78745504c247169848df0958287be9
Merge topic 'context-interactor-style-timer' into master

914c6827 BUG: Fix bug #14378, ensure observer is removed in dtor