atlas: cleanup stop log message (#1136)

The `step` variable is a duration and the toString indicates
the units. Remove the `ms` in the log message which are
confusing and lead to message like `PT1Mms`.

spectator-reg-atlas/src/main/java/com/netflix/spectator/atlas/AtlasRegistry.java

@@ -196,7 +196,7 @@ public void stop() {
       // Shutdown background tasks to collect data
       scheduler.shutdown();
       scheduler = null;
-      logger.info("stopped collecting metrics every {}ms reporting to {}", step, uri);
+      logger.info("stopped collecting metrics every {} reporting to {}", step, uri);
 
       // Flush data to Atlas
       try {