Avoid multiple validation of same property (relatedEntity here) by avoiding redefinition

[hamdan-ahmad-lb]

This issue is strictly related to before-interop/anomalieAdresse#133 and should be resolved together.

Currently, TroubleTicket, AnomalieAdresseBase, AnomalieAdresseNewBuilding, AnomalieAdresseUpdate, and AnomalieAdresseUpdateNbLogements all defines the relatedEntity property.

If we want to have polymorphism, this leads to have "cascading validation" more than once for the relatedEntity. This will cause the validation to always fail in any interface generated using codegen.

Normally, we should have a single source of truth, and this is highlighted in the official best practices:
https://learn.openapis.org/best-practices.html#keep-a-single-source-of-truth

that's why we should remove the definition of relatedEntity from parents and define it only in the "leaves"