remove code that ignores missing datalists when importing

cannot reproduce the error with the following basket:

{
    "DataList": {
        "missing_list": {
            "list_name": "missing_list",
            "owner": "icinga-admin",
            "guid": "fdd809b4-6cca-49b0-8c4e-b53c89241482",
            "originalId": "990",
            "entries": [
                {
                    "entry_name": "entry 1",
                    "entry_value": "entry 1",
                    "format": "string",
                    "allowed_roles": null
                }
            ]
        }
    },
    "Datafield": {
        "991": {
            "varname": "missing test datafield",
            "caption": "missing test datafield",
            "description": null,
            "datatype": "Icinga\\Module\\Director\\DataType\\DataTypeDatalist",
            "format": null,
            "guid": "e155b00e-3a8f-4f09-aebd-1105ef1fd044",
            "originalId": "991",
            "settings": {
                "data_type": "array",
                "datalist": "missing_list"
            }
        }
    }
}