Bump Guava to 21.0

Change-Id: Id81705773d191db6a18153d8b2dd4abd2bfd0e60
diff --git a/apps/newoptical/src/main/java/org/onosproject/newoptical/OpticalPathProvisioner.java b/apps/newoptical/src/main/java/org/onosproject/newoptical/OpticalPathProvisioner.java
index 245a90f..b25d568 100644
--- a/apps/newoptical/src/main/java/org/onosproject/newoptical/OpticalPathProvisioner.java
+++ b/apps/newoptical/src/main/java/org/onosproject/newoptical/OpticalPathProvisioner.java
@@ -30,7 +30,6 @@
 import org.onlab.graph.ScalarWeight;
 import org.onlab.graph.Weight;
 import org.onlab.util.Bandwidth;
-import org.onlab.util.GuavaCollectors;
 import org.onlab.util.KryoNamespace;
 import org.onlab.util.Tools;
 import org.onosproject.cluster.ClusterService;
@@ -274,7 +273,7 @@
     public Collection<OpticalConnectivity> listConnectivity() {
         return connectivityMap.values().stream()
             .map(Versioned::value)
-            .collect(GuavaCollectors.toImmutableList());
+            .collect(ImmutableList.toImmutableList());
     }
 
     @Override