Fix false positive unit test for Observers
The observer associated with a key returned by smtk::common::Observers::insert() will be removed from the Observers if the key is destroyed
FYI @bob.obara @dcthomp
The observer associated with a key returned by smtk::common::Observers::insert() will be removed from the Observers if the key is destroyed
FYI @bob.obara @dcthomp