Don't retrieve settings illegal on index creation

Context

Link to ticket: https://enrise.atlassian.net/browse/SAAS-1110 Main MR: https://gitlab.enrise.com/MatchMinds/SAAS-Sitesearch/merge_requests/915

We are upgrading to elasticsearch 7. During this upgrade we had problems in the upgrade script. Elasticsearch 7 is stricter in checking what arguments are provided when creating a new index.

What has been done

• Delete setting that not allowed to be used when creating a new index

How to test

• In the test of https://gitlab.enrise.com/MatchMinds/SAAS-Sitesearch/merge_requests/915 we upgrade an index. This tests the changes in this MR

Notes

• Maybe we should rename getMapping to indicate that we don't actually get the whole mapping. But I can't think of a good name. getPartialMapping or getRelevantMappingParts don't feel very eloquent. I think it's OK like this.