Remove command component from Calculator Tutorial

Instead of composing with a command component, the `calculator` world could export `wasi:cli/run` itself:
```
package docs:calculator@0.1.0;

interface calculate {
enum op {
add,
}
eval-expression: func(op: op, x: u32, y: u32) -> u32;
}

world calculator {
export calculate;
import docs:adder/add@0.1.0;
}

world app {
import calculate;
export wasi:cli/run; <--- suggested addition
}
```