Disjunctive facets may break when used with signed search keys

Hello! I'm having trouble to make disjunctive facets work with signed search keys.

I think it's related to this: https://github.com/elastic/search-ui/issues/347

On this [line](https://github.com/elastic/app-search-javascript/blob/master/src/client.js#L174), I see that we are cleaning up request filters, but on my case filters are still sent this way:

Which seems to cause some kind of issue with AppSearch using signed search keys.
```
"alerts":[{"code":5001,"message":"Degraded search results","link":"https://swiftype.com/documentation/app-search/alerts#5001"}]
```

What I tried:
* If I remove filters on that request **it works** even with a signed search key
* Also if I change the signed search key to a normal search key, **it also works**.

**One last thing**
My search key only applies one filter:

Any help is much appreciated!!
Thanks