Remove local discovery from migration docs

This commit removes mention of local discovery as a replacement for
setting node.local to true.

Relates #22064

docs/reference/migration/migrate_5_0/settings.asciidoc

@@ -31,8 +31,8 @@ The `node.add_id_to_custom_path` was renamed to `add_lock_id_to_custom_path`.
 The default for the `node.name` settings is now the first 7 characters of the node id,
 which is in turn a randomly generated UUID.
 
-The settings `node.mode` and `node.local` are removed. Local mode should be configured via
-`discovery.type: local` and `transport.type:local`. In order to disable _http_ please use `http.enabled: false`
+The settings `node.mode` and `node.local` are removed. Local mode should be configured via `transport.type: local`. In
+order to disable HTTP please use `http.enabled: false`
 
 ==== Node attribute settings
 

docs/reference/migration/migrate_5_1.asciidoc

@@ -32,6 +32,12 @@ aliases with invalid names is also no longer supported.
 The Log4j dependency has been upgraded from version 2.6.2 to version 2.7. If you're using the transport client in your
 application, you should update your Log4j dependencies accordingly.
 
+[float]
+==== Local discovery has been removed
+
+Local discovery has been removed; this discovery implementation was used internally in the tribe service and for tests
+that ran multiple nodes inside the same JVM. This means that setting `discovery.type` to `local` will fail on startup.
+
 [[breaking_51_plugin_api]]
 [float]
 === Plugin API changes