Polish "Use constants for HTTP headers"

See gh-17199

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/endpoint/web/WebEndpointAutoConfiguration.java

@@ -52,7 +52,6 @@ import org.springframework.boot.context.properties.EnableConfigurationProperties
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
-import org.springframework.http.MediaType;
 
 /**
  * {@link EnableAutoConfiguration Auto-configuration} for web {@link Endpoint @Endpoint}
@@ -68,8 +67,7 @@ import org.springframework.http.MediaType;
 @EnableConfigurationProperties(WebEndpointProperties.class)
 public class WebEndpointAutoConfiguration {
 
-	private static final List<String> MEDIA_TYPES = Arrays.asList(ActuatorMediaType.V2_JSON,
-			MediaType.APPLICATION_JSON_VALUE);
+	private static final List<String> MEDIA_TYPES = Arrays.asList(ActuatorMediaType.V2_JSON, "application/json");
 
 	private final ApplicationContext applicationContext;