Remove FIXME on retain in ReactorServerHttpRequest

The converters release so this is the right thing to do, not a
temporary fix.

spring-web-reactive/src/main/java/org/springframework/http/server/reactive/ReactorServerHttpRequest.java

@@ -89,9 +89,7 @@ public class ReactorServerHttpRequest extends AbstractServerHttpRequest {
 
 	@Override
 	public Flux<DataBuffer> getBody() {
-		return this.channel.receive()
-		                   .retain() //FIXME Rogue reference holding
-				.map(dataBufferFactory::wrap);
+		return this.channel.receive().retain().map(this.dataBufferFactory::wrap);
 	}
 
 }