Problem

The fields_matched field does not make sense on the single results view as no search has been executed that could be matched.

Description

Exclude the fields_matched field on single result serializer.

One way to do this is to remove fields_matched from the basic MediaSerializer and have an additional subclass called SearchResultSerializer (or similar) that adds the field.

The field is currently always empty on the single results page. Removing it entirely would cause a backwards compatibility issue, so this is probably not possible to implement until we have #662 completed.