Use `let` for stats in budget stats spec
Use `let` for stats in budget stats spec

The rest of the `before` block still uses instance variables, but at
least the rest of the file doesn't use instance variables anymore.

usabi/consul_san_borondon,usabi/consul_san_borondon,consul/consul,AyuntamientoPuertoReal/decidePuertoReal,consul/consul,consul/consul,AyuntamientoPuertoReal/decidePuertoReal,consul/consul,AyuntamientoPuertoReal/decidePuertoReal,usabi/consul_san_borondon,usabi/consul_san_borondon,consul/consul