Remove old workaround / fix bug in sb.interpolate

[liamgriffiths]

Before using sb.interpolate when the interpolation items were next to each other a prior workaround was not including them into the Future properly.

A simplest example that demonstrates this might be,

const a = new Box({ value: sb.interpolate`${"x"}` });
const res = await substrate.run(a);
console.log(JSON.stringify(res.json, null, 2));

// outputs
{
  "data": {
    "node1_S2ZNfqWT": {
      "value": ""
    }
  }
}

With this patch these odd cases should work properly.