LPS-35643 Cleaning up user staged model data handler and related changes

Hey Julio,

Remember we have talked about this earlier. In favor of validating the users upon import @KocsisDaniel has implemented a UserSMDH and he created an interface, the StagedAuditedModel.

In the meantime a decision has been made that this is not used anymore, so I'm sending the cleanup to you now.

These changes are making the infrastructure more complex, and they are useless.

Thanks,

Máté