Replacing data nodes instructions are dangerous

[lesam]

When replacing data nodes, it says to just run update-data to let a new node take its place. This is problematic:

1. If there is any data with RF<2, it gets lost if you do this. I think this needs a big warning.
2. AE is off by default but these instructions assume it is on
3. If the data node is currently working (not a failed/lost disk), users could also just copy data over and use the instructions from https://docs.influxdata.com/enterprise_influxdb/v1.9/administration/manage/renaming/#rename-data-nodes , which seems better than waiting for AE to fix things.

Relevant URLs

(https://docs.influxdata.com/enterprise_influxdb/v1.9/administration/manage/clusters/replacing-nodes/#replace-data-nodes-in-an-influxdb-enterprise-cluster)

@timhallinflux FYI