[DOCS] Remove unused upgrade doc files

docs/reference/redirects.asciidoc

@@ -1811,10 +1811,39 @@ even if you opt to perform a full-cluster restart instead of a rolling upgrade.
 For more information about upgrading, see 
 {stack-ref}/upgrading-elastic-stack.html[Upgrading to Elastic {version}].
 
-role="exclude",id="rolling-upgrade"]
+[role="exclude",id="rolling-upgrades"]
 === Rolling upgrade
 
 When upgrading to {es} 8.0 and later, you must first upgrade to {prev-major-last}
 whether you opt to perform a rolling upgrade (upgrade one node at a time) or a full-cluster restart upgrade.
 For more information about upgrading, see 
 {stack-ref}/upgrading-elastic-stack.html[Upgrading to Elastic {version}].
+
+[role="exclude",id="reindex-upgrade"]
+=== Reindex before upgrading
+
+//tag::upgrade-reindex[]
+Before upgrading to {es} 8.0 and later, you must reindex any indices created in
+a 6.x version. We recommend you use the Upgrade Assistant to guide you
+through this process.
+
+For more information about upgrading, see 
+{stack-ref}/upgrading-elastic-stack.html[Upgrading to Elastic {version}].
+//end::upgrade-reindex[]
+
+For more information about reindexing, see <<docs-reindex>>.
+
+[role="exclude",id="reindex-upgrade-inplace"]
+=== Reindex in place
+
+include::redirects.asciidoc[tag=upgrade-reindex]
+
+For more information about reindexing, see <<docs-reindex>>.
+
+[role="exclude",id="reindex-upgrade-remote"]
+=== Reindex from a remote cluster
+
+include::redirects.asciidoc[tag=upgrade-reindex]
+
+For more information about reindexing from a remote cluster, see
+<<reindex-from-remote>>.