Removes Zipkin dependency from all tests (#1645)

Brave's SpanHandler can report natively in other formats which have different
constraints than Zipkin and often extensions to the data model.

This change ports all tests away from Zipkin's types so that it is more clear
what's actually recorded vs what's a side-effect of Zipkin conversion.

This removes `BlockingQueueSpanReporter` which was never released, also.

tests/spring-cloud-sleuth-instrumentation-rxjava-tests/pom.xml

@@ -60,6 +60,11 @@
 			<artifactId>spring-boot-starter-test</artifactId>
 			<scope>test</scope>
 		</dependency>
+		<dependency>
+			<groupId>io.zipkin.brave</groupId>
+			<artifactId>brave-tests</artifactId>
+			<scope>test</scope>
+		</dependency>
 		<dependency>
 			<groupId>org.awaitility</groupId>
 			<artifactId>awaitility</artifactId>