Remove outdated XML formatter documentation

CHANGELOG.md

@@ -20,6 +20,7 @@
 
 #### Fixes
 
+* [#2412](https://github.com/ruby-grape/grape/pull/2412): Update outdated documentation for XML formatter - [@eriklovmo](https://github.com/eriklovmo)
 * [#2375](https://github.com/ruby-grape/grape/pull/2375): Fix setter methods for `Grape::Router::AttributeTranslator` - [@Jell](https://github.com/Jell).
 * [#2370](https://github.com/ruby-grape/grape/pull/2370): Remove route_xyz method_missing deprecation - [@ericproulx](https://github.com/ericproulx).
 * [#2372](https://github.com/ruby-grape/grape/pull/2372): Fix `declared` method for hash params with overlapping names - [@jcagarcia](https://github.com/jcagarcia).

README.md

@@ -3100,7 +3100,7 @@ end
 Built-in formatters are the following.
 
 * `:json`: use object's `to_json` when available, otherwise call `MultiJson.dump`
-* `:xml`: use object's `to_xml` when available, usually via `MultiXml`, otherwise call `to_s`
+* `:xml`: use object's `to_xml` when available, usually via `MultiXml`
 * `:txt`: use object's `to_txt` when available, otherwise `to_s`
 * `:serializable_hash`: use object's `serializable_hash` when available, otherwise fallback to `:json`
 * `:binary`: data will be returned "as is"