Revert "Add PR #31739 to 7.2 breaking changes doc (#38740)"

This reverts commit c429ec4.

docs/migration/migrate_7_2.asciidoc

@@ -13,7 +13,6 @@ coming[7.2.0]
 
 
 * <<breaking_72_index_pattern_changes>>
-* <<breaking_72_saved_objects_migration_changes>>
 
 
 [float]
@@ -33,17 +32,6 @@ time-based index patterns to a wildcard pattern to prepare for this change.
 on the root wildcard term. For example, a query on an index pattern such as 
 `[logstash-]YYYY.MM.DD` will now query all indices that match `logstash-*`.
 
-[float]
-[[breaking_72_saved_objects_migration_changes]]
-=== Saved object migration changes
-
-[float]
-==== New error is thrown when a plugin defines a migration for a mapping it doesn't define or own
-*Details:* Kibana will now throw an error on startup if a plugin has defined
-a saved object migration inside a plugin that doesn't define or own the mappings to.
-
-*Impact:* If you define migrations within your plugin but the mappings is
-owned by another plugin, Kibana will no longer allow that and not start up.
 
 //NOTE: The notable-breaking-changes tagged regions are re-used in the
 //Installation and Upgrade Guide