NIFI-5414 Fixed checkstyle error due to unused import.
diff --git a/nifi-nar-bundles/nifi-framework-bundle/nifi-framework/nifi-framework-core/src/main/java/org/apache/nifi/controller/service/ServiceStateTransition.java b/nifi-nar-bundles/nifi-framework-bundle/nifi-framework/nifi-framework-core/src/main/java/org/apache/nifi/controller/service/ServiceStateTransition.java
index e78f6c6..26e3b82 100644
--- a/nifi-nar-bundles/nifi-framework-bundle/nifi-framework/nifi-framework-core/src/main/java/org/apache/nifi/controller/service/ServiceStateTransition.java
+++ b/nifi-nar-bundles/nifi-framework-bundle/nifi-framework/nifi-framework-core/src/main/java/org/apache/nifi/controller/service/ServiceStateTransition.java
@@ -21,7 +21,6 @@
 
 import java.util.ArrayList;
 import java.util.List;
-import java.util.Set;
 import java.util.concurrent.CompletableFuture;
 
 public class ServiceStateTransition {