Proper squashing of rc20 blockstores

[Mingela]

Although upgrading to rc20 seems to work fine, when trying to squash a blockstore for rc20 there is the issue occurs. (Managed to face just this for now).

For any asset definition registration there is a transfer instruction appended (though it does not exist in the original store) forming a Pair:

{
                "Pair": {
                    "left_instruction": {
                        "Register": {
                            "NewAssetDefinition": {
                                "id": "credit#admin",
                                "value_type": "Quantity",
                                "mintable": "Infinitely",
                                "logo": null,
                                "metadata": {}
                            }
                        }
                    },
                    "right_instruction": {
                        "Transfer": {
                            "source_id": {
                                "AccountId": "genesis@genesis"
                            },
                            "object": {
                                "AssetDefinition": {
                                    "id": "credit#admin",
                                    "value_type": "Quantity",
                                    "mintable": "Infinitely",
                                    "logo": null,
                                    "metadata": {},
                                    "owned_by": "genesis@genesis"
                                }
                            },
                            "destination_id": {
                                "AccountId": "genesis@genesis"
                            }
                        }
                    }
                }
            }

Obviously the right instruction is not valid (transfer to myself) so that Iroha can't start