Bidirectional association between same class: old model reuses not removed when properties changed

[Matthias Schoettle]

Steps to reproduce:

1. Create class A
2. Create a reflexive association on A
3. Change the multiplicity on of the ends to 0..*
4. Try to save

The save will fail due to uncontained references. The reason is that the model reuse is not removed, so there will be 3 in total now. If also the other end is changed, there will be 4 in total.