Remove deprecated getLeaderBoard() API from LeadershipService

Change-Id: I009e1ae26faef3950a7a5e997376783895f575f2
diff --git a/core/net/src/main/java/org/onosproject/cluster/impl/LeadershipManager.java b/core/net/src/main/java/org/onosproject/cluster/impl/LeadershipManager.java
index 19e85bf..07d8419 100644
--- a/core/net/src/main/java/org/onosproject/cluster/impl/LeadershipManager.java
+++ b/core/net/src/main/java/org/onosproject/cluster/impl/LeadershipManager.java
@@ -18,7 +18,9 @@
 import static org.slf4j.LoggerFactory.getLogger;
 
 import java.util.Map;
+import java.util.Set;
 
+import com.google.common.base.Objects;
 import org.apache.felix.scr.annotations.Activate;
 import org.apache.felix.scr.annotations.Component;
 import org.apache.felix.scr.annotations.Deactivate;
@@ -84,6 +86,11 @@
     }
 
     @Override
+    public Set<String> ownedTopics(NodeId nodeId) {
+        return Maps.filterValues(store.getLeaderships(), v -> Objects.equal(nodeId, v.leaderNodeId())).keySet();
+    }
+
+    @Override
     public Leadership runForLeadership(String topic) {
         return store.addRegistration(topic);
     }