Remove last_reviewed_on/review_in fields

Whilst this change happened on 29th October 2020, the commit date has been
backdated so that the 'last_updated' behaviour is unaffected. We don't want
to give a misleading impression that this document is more up to date than
it is because of the side-effect of removing some of its frontmatter.

source/manual/reindex-elasticsearch.html.md

@@ -4,8 +4,6 @@ title: Reindex an Elasticsearch index
 section: Publishing
 layout: manual_layout
 parent: "/manual.html"
-last_reviewed_on: 2020-08-10
-review_in: 6 months
 related_applications: [search-api]
 ---