Merge pull request #99886 from skopacz1/OSDOCS-16352

OSDOCS#16352: removing external platform from list

Author: mburke5678

nodes/nodes/nodes-nodes-adding-node-iso.adoc

@@ -28,7 +28,6 @@ The following platforms are supported for this method of adding nodes:
 * `vsphere`
 * `nutanix`
 * `none`
-* `external`
 
 [id="supported-architectures_{context}"]
 == Supported architectures