Remove reference to multiple fields with one name (#31127)

If there is only one type per index then each field's name is unique.

docs/reference/mapping/params/fielddata.asciidoc

@@ -100,11 +100,6 @@ PUT my_index/_mapping/_doc
 <1> The mapping that you specify for `my_field` should consist of the existing
     mapping for that field, plus the `fielddata` parameter.
 
-TIP: The `fielddata.*` parameter must have the same settings for fields of the
-same name in the same index.  Its value can be updated on existing fields
-using the <<indices-put-mapping,PUT mapping API>>.
-
-
 [[field-data-filtering]]
 ==== `fielddata_frequency_filter`