- Ensure with a test that iterating a ReferenceSet after a   referred object has been removed won't include the object. - Removed duplicated test.
- Ensure with a test that iterating a ReferenceSet after a
  referred object has been removed won't include the object.
- Removed duplicated test.

petrhosek/storm,PyMamba/mamba-storm,petrhosek/storm,PyMamba/mamba-storm,petrhosek/storm,PyMamba/mamba-storm