Revert "Docs for preventing migrations failing for unknown saved obje…

…ct types"

This reverts commit 561d0b7.

Oops shouldn't have pushed this to main directly

docs/setup/upgrade/upgrade-migrations.asciidoc

@@ -58,29 +58,6 @@ complete the upgrade migration before bringing up the remaining instances.
 ==== Preventing migration failures
 Review the common causes of {kib} upgrade failures and how to prevent them.
 
-[float]
-====== Documents were found for unknown saved object types
-Migrations will fail if saved objects were found which belong to an unknown
-saved object type. This could be caused by writing malformed documents directly
-to the Elasticsearch index, or by disabling a plugin that had previously
-created a saved object.
-
-We recommend using the <<upgrade-assistant,Upgrade Assistant>> to discover and
-remedy any unknown saved object types. In addition to the upgrade assistant, 
-{kib} version 7.17.0 deployments containing unknown saved object types will 
-also log the following warning message:
-
-[source,sh]
---------------------------------------------
-CHECK_UNKNOWN_DOCUMENTS Upgrades will fail for 8.0+ because documents were found for unknown saved object types. To ensure that upgrades will succeed in the future, either re-enable plugins or delete these documents from the ".kibana_7.17.0_001" index after the current upgrade completes.
---------------------------------------------
-
-If you fail to remedy this, your upgrade to 8.0+ will fail with a message like:
-[source,sh]
---------------------------------------------
-Unable to complete saved object migrations for the [.kibana] index: Migration failed because documents were found for unknown saved object types. To proceed with the migration, please delete these documents from the ".kibana_7.17.0_001" index.
---------------------------------------------
-
 [float]
 ===== timeout_exception or receive_timeout_transport_exception
 There is a known issue in 7.12.0 for users who tried the {fleet} beta.