In #33933 we disallowed changing the `enabled` parameter in object mappings.
However, the fix didn't cover the root object mapper. This PR adjusts the change
to also include the root mapper and clarifies the error message.
This setting is not documented and has dubious value since it means
there can be nodes in the cluster (non-data and non-master nodes) that
do not have persistent node IDs. This does not have any use cases so
this commit removes the setting.