Fix OAuth2BodyExtractorsTests for JDK9

Issue: gh-5475

oauth2/oauth2-core/src/test/java/org/springframework/security/oauth2/core/web/reactive/function/OAuth2BodyExtractorsTests.java

@@ -27,7 +27,6 @@ import org.springframework.http.codec.DecoderHttpMessageReader;
 import org.springframework.http.codec.FormHttpMessageReader;
 import org.springframework.http.codec.HttpMessageReader;
 import org.springframework.http.codec.json.Jackson2JsonDecoder;
-import org.springframework.http.codec.xml.Jaxb2XmlDecoder;
 import org.springframework.http.server.reactive.ServerHttpResponse;
 import org.springframework.mock.http.client.reactive.MockClientHttpResponse;
 import org.springframework.security.oauth2.core.OAuth2AccessToken;
@@ -60,7 +59,6 @@ public class OAuth2BodyExtractorsTests {
 		final List<HttpMessageReader<?>> messageReaders = new ArrayList<>();
 		messageReaders.add(new DecoderHttpMessageReader<>(new ByteBufferDecoder()));
 		messageReaders.add(new DecoderHttpMessageReader<>(StringDecoder.allMimeTypes()));
-		messageReaders.add(new DecoderHttpMessageReader<>(new Jaxb2XmlDecoder()));
 		messageReaders.add(new DecoderHttpMessageReader<>(new Jackson2JsonDecoder()));
 		messageReaders.add(new FormHttpMessageReader());