Tidy up some dependencies

Removes wiremock as a test dependency in core (which created more
issues than you might expect because Tomcat and Jetty don't treay
HTTP headers in the same way apparently).

Also moves the spring-messaging dependency to where it is needed
in sleuth stream.

spring-cloud-sleuth-samples/spring-cloud-sleuth-sample-zipkin-stream/pom.xml

@@ -35,7 +35,6 @@
 	<properties>
 		<docker.image.prefix>springio</docker.image.prefix>
 		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-		<zipkin-ui.version>1.39.8</zipkin-ui.version>
 		<java.version>1.8</java.version>
 		<sonar.skip>true</sonar.skip>
 	</properties>
@@ -57,7 +56,6 @@
 		<dependency>
 			<groupId>io.zipkin</groupId>
 			<artifactId>zipkin-ui</artifactId>
-			<version>${zipkin-ui.version}</version>
 		</dependency>
 		<dependency>
 			<groupId>org.springframework.integration</groupId>