Remove type: objekt from property transportUnitIdentifierReference

[larsolofsson]

Property transportUnitIdentifierReference could be simplified.

Current constract

                    transportUnitIdentifierReference:
                      type: object
                      unevaluatedProperties: false
                      required:
                        - value
                      properties:
                        value:
                          type: string
                          minLength: 1

could be changed to

                    transportUnitIdentifierReference:
                          type: string
                          minLength: 1