Migrate Karate to use closeActive() to close outstanding spans

Author: mcculls

dd-java-agent/instrumentation/karate/src/main/java/datadog/trace/instrumentation/karate/KarateTracingHook.java

@@ -221,11 +221,7 @@ public void afterStep(StepResult result, ScenarioRuntime sr) {
       return;
     }
 
-    AgentScope scope = AgentTracer.activeScope();
-    if (scope != null) {
-      scope.close();
-    }
-
+    AgentTracer.closeActive();
     span.finish();
   }