Removed docs from mapper-attachment about copy_to

Closes #18361

docs/plugins/mapper-attachments.asciidoc

@@ -173,38 +173,6 @@ In the above example, the actual content indexed is mapped under `fields` name `
 it will only be available in the `_all` field. The other fields map to their respective metadata names, but there is no
 need to specify the `type` (like `string` or `date`) since it is already known.
 
-[[mapper-attachments-copy-to]]
-==== Copy To feature
-
-If you want to use https://www.elastic.co/guide/en/elasticsearch/reference/current/copy-to.html[copy_to]
-feature, you need to define it on each sub-field you want to copy to another field:
-
-[source,js]
---------------------------
-PUT /test/person/_mapping
-{
-  "person": {
-    "properties": {
-      "file": {
-        "type": "attachment",
-        "fields": {
-          "content": {
-            "type": "string",
-            "copy_to": "copy"
-          }
-        }
-      },
-      "copy": {
-        "type": "string"
-      }
-    }
-  }
-}
---------------------------
-// AUTOSENSE
-
-In this example, the extracted content will be copy as well to `copy` field.
-
 [[mapper-attachments-querying-metadata]]
 ==== Querying or accessing metadata