Removes 9.0 release notes and 9.0 rc1 upgrade docs

Author: KOTungseth

docs/en/install-upgrade/index.asciidoc

@@ -14,48 +14,4 @@ include::installing-stack-demo-secure.asciidoc[]
 
 include::air-gapped-install.asciidoc[]
 
-include::serverless-changelog.asciidoc[]
-
-include::breaking.asciidoc[]
-
-include::release-notes/release-notes.asciidoc[leveloffset=+1]
-
-include::release-notes/release-notes-beats.asciidoc[leveloffset=+2]
-
-include::release-notes/release-notes-security.asciidoc[leveloffset=+2]
-
-include::release-notes/release-notes-elasticsearch.asciidoc[leveloffset=+2]
-
-include::release-notes/release-notes-fleet-agent.asciidoc[leveloffset=+2]
-
-include::release-notes/release-notes-kibana.asciidoc[leveloffset=+2]
-
-include::release-notes/release-notes-logstash.asciidoc[leveloffset=+2]
-
-include::upgrading-stack.asciidoc[]
-
-include::upgrade-orchestrator.asciidoc[]
-
-include::upgrade-deployment-cluster.asciidoc[]
-
-include::upgrading-stack-cloud.asciidoc[]
-
-include::upgrade-on-ece.asciidoc[]
-
-include::upgrade-on-eck.asciidoc[]
-
-include::upgrading-stack-on-prem.asciidoc[]
-
-include::upgrading-elasticsearch.asciidoc[]
-
-include::upgrading-kibana.asciidoc[]
-
-// include::upgrading-logstash.asciidoc[]
-
-// include::upgrading-beats.asciidoc[]
-
-// include::upgrading-APM.asciidoc[]
-
-// include::upgrading-agent.asciidoc[]
-
 include::redirects.asciidoc[]