Revert changes to headers

Span name is properly optional in Zipkin, but it makes the logs
in Sleuth a lot easier to read. Process ID is optional because it
is a Sleuth feature, but it seems useful.

This reverts commit b4d71727bf.

spring-cloud-sleuth-samples/spring-cloud-sleuth-sample-zipkin/src/main/java/org/springframework/cloud/sleuth/sample/SampleZipkinApplication.java

@@ -43,11 +43,6 @@ public class SampleZipkinApplication {
 		return new AlwaysSampler();
 	}
 
-	@Bean
-	public SampleController sampleController() {
-		return new SampleController();
-	}
-
 	public static void main(String[] args) {
 		SpringApplication.run(SampleZipkinApplication.class, args);
 	}