Fix index mapping parameter option (#9023)

Signed-off-by: Archer <[email protected]>

_field-types/mapping-parameters/index.md

@@ -24,5 +24,5 @@ Parameter | Description
 `format` | Specifies the date format for date fields. There is no default value for this parameter. Allowed values are any valid date format string, such as `yyyy-MM-dd` or `epoch_millis`.
 `ignore_above` | Skips indexing values that exceed the specified length. Default value is `2147483647`, which means that there is no limit on the field value length. Allowed values are any positive integer.
 `ignore_malformed` | Specifies whether malformed values should be ignored. Default value is `false`, which means that malformed values are not ignored. Allowed values are `true` or `false`.
-`index` | Specifies whether a field should be indexed. Default value is `true`, which means that the field is indexed. Allowed values are `true`, `false`, or `not_analyzed`.
+`index` | Specifies whether a field should be indexed. Default value is `true`, which means that the field is indexed. Allowed values are `true` or `false`.
 `index_options` | Specifies what information should be stored in an index for scoring purposes. Default value is `docs`, which means that only the document numbers are stored in the index. Allowed values are `docs`, `freqs`, `positions`, or `offsets`.