**TL;DR** Elasticsearch defaults to sorting by `_score` and this is what
we want so remove all the explicit sorting.

At present some searches are being sorted by `_score` (ie. the relevance
score) while others are being first sorted by `updated_at` then
`_score`.

There doesn't really appear to be any good reason to use `updated_at` as
the primary sort followed by `_score` since this will bury the most
relevant matches behind lots of recent matches. Using sort in this way
will only ever sort by `_score` if the `updated_at` was equal but this
is basically never going to happen since these are timestamps so
`_score` in practice is never factoring in to the sorting which probably
was never the intent here.

Since the [default sorting is by
score](https://www.elastic.co/guide/en/elasticsearch/guide/master/sorting.html)
we can leave it out of all queries.

We can in future look into whether or not we want recency to factor into
the sorting using more advanced tools like
[`function_score`](https://www.elastic.co/guide/en/elasticsearch/guide/current/function-score-query.html)
but for now sorting just by relevance is better than sorting just by
`updated_at`.