Docs: Removed a reference to index_name from the array mapping page

docs/reference/mapping/types/array-type.asciidoc

@@ -67,8 +67,3 @@ the fact that the following JSON document is perfectly fine:
 }
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-Note also, that thanks to the fact that we used the `index_name` to use
-the non plural form (`tag` instead of `tags`), we can actually refer to
-the field using the `index_name` as well. For example, we can execute a
-query using `tweet.tags:wow` or `tweet.tag:wow`. We could, of course,
-name the field as `tag` and skip the `index_name` all together).