[8.15] Removes non-backup rollback from upgrade kibana (#189011) (#18…

…9088)

# Backport

This will backport the following commits from `main` to `8.15`:
- [Removes non-backup rollback from upgrade kibana
(#189011)](#189011)

<!--- Backport version: 9.4.3 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

<!--BACKPORT [{"author":{"name":"Christiane (Tina)
Heiligers","email":"[email protected]"},"sourceCommit":{"committedDate":"2024-07-24T14:51:24Z","message":"Removes
non-backup rollback from upgrade kibana (#189011)\n\nFIx
https://github.com/elastic/kibana/issues/158117\r\n\r\nRemoves section
on rolling back without a snapshot.\r\n\r\nThe changes made to kibana
saved objects migration make the process of\r\nrolling back without a
snapshot too complex for customers to do alone.\r\nFurthermore, rolling
back without a snapshot is not recommended or\r\nsupported.\r\n\r\nSee
the changes on
`master`\r\n[here](https://kibana_bk_189011.docs-preview.app.elstc.co/guide/en/kibana/master/upgrade-migrations-rolling-back.html)\r\n\r\nCo-authored-by:
Elastic Machine
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non-backup rollback from upgrade
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non-backup rollback from upgrade kibana (#189011)\n\nFIx
https://github.com/elastic/kibana/issues/158117\r\n\r\nRemoves section
on rolling back without a snapshot.\r\n\r\nThe changes made to kibana
saved objects migration make the process of\r\nrolling back without a
snapshot too complex for customers to do alone.\r\nFurthermore, rolling
back without a snapshot is not recommended or\r\nsupported.\r\n\r\nSee
the changes on
`master`\r\n[here](https://kibana_bk_189011.docs-preview.app.elstc.co/guide/en/kibana/master/upgrade-migrations-rolling-back.html)\r\n\r\nCo-authored-by:
Elastic Machine
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non-backup rollback from upgrade kibana (#189011)\n\nFIx
https://github.com/elastic/kibana/issues/158117\r\n\r\nRemoves section
on rolling back without a snapshot.\r\n\r\nThe changes made to kibana
saved objects migration make the process of\r\nrolling back without a
snapshot too complex for customers to do alone.\r\nFurthermore, rolling
back without a snapshot is not recommended or\r\nsupported.\r\n\r\nSee
the changes on
`master`\r\n[here](https://kibana_bk_189011.docs-preview.app.elstc.co/guide/en/kibana/master/upgrade-migrations-rolling-back.html)\r\n\r\nCo-authored-by:
Elastic Machine
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BACKPORT-->

Co-authored-by: Christiane (Tina) Heiligers <[email protected]>

docs/setup/upgrade/rollback-migration.asciidoc

@@ -30,40 +30,3 @@ POST _snapshot/my_repository/my_snapshot_2099.05.06/_restore
 --------------------------------------------
 <1> Exclude all indices and data streams from the restore operation to ensure that only the {kib} system indices included in the {kib} feature state will be restored.
 . Start all {kib} instances on the older version you want to rollback to.
-
-[float]
-==== (Not supported) Roll back without a backup snapshot
-
-WARNING: Rolling back without a backup snapshot is not supported and will be removed in a future version of {kib}.
-
-. To make sure no {kib} instances are performing an upgrade migration, shut down all {kib} instances.
-. {ref}/snapshots-take-snapshot.html[Take a snapshot] that includes the `kibana` feature state. By default, snapshots include the `kibana` feature state.
-. Delete the version-specific indices created by the failed upgrade migration.
-+
-For example, to rollback from a failed upgrade
-to v7.12.0, enter:
-+
-[source,sh]
---------------------------------------------
-DELETE /.kibana_7.12.0_*,.kibana_task_manager_7.12.0_*
---------------------------------------------
-
-. Inspect the output of `GET /_cat/aliases`.
-+
-If the `.kibana` or `.kibana_task_manager` aliases are missing, you must create them manually.
-Find the latest index from the output of `GET /_cat/indices` and create the missing alias to point to the latest index.
-For example, if the `.kibana` alias is missing, and the latest index is `.kibana_3`, create a new alias using:
-+
-[source,sh]
---------------------------------------------
-POST /.kibana_3/_aliases/.kibana
---------------------------------------------
-
-. To remove the write block from the roll back indices, enter:
-+
-[source,sh]
---------------------------------------------
-PUT /.kibana,.kibana_task_manager/_settings {"index.blocks.write": false}
---------------------------------------------
-
-. Start {kib} on the older version you want to roll back to.