remove TransferRequest assetId

[ndr-brt]

Feature Request

As discussed during #4260 , assetId field in TransferRequest is not really needed, because the assetId can be obtained from the ContractAgreement targeted by the contractId.
Removing it the API will be easier and there won't be no need to validate it.

Which Areas Would Be Affected?

transfer process api

Why Is the Feature Desired?

cleanup

Solution Proposal

remove the field from TransferRequest, read it from ContractAgreement, deprecate the field on the API and print a deprecation warning when it's used