Fix exclude filter to not exclude MediaType

This commit removes MediaType from the list of exclude types as it looks
like an error: MediaType has a constructor taking a `String` and binding
works fine with it.

This has the effect of properly generating the metadata for the only key
that Spring Boot exposes with a MediaType type:
spring.data.rest.default-media-type.

Closes gh-11568

spring-boot-tools/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/TypeExcludeFilter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2015 the original author or authors.
+ * Copyright 2012-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -46,7 +46,6 @@ class TypeExcludeFilter {
 		add("org.apache.tomcat.jdbc.pool.Validator");
 		add("org.flywaydb.core.api.callback.FlywayCallback");
 		add("org.flywaydb.core.api.resolver.MigrationResolver");
-		add("org.springframework.http.MediaType");
 	}
 
 	private void add(String className) {