Eliminate unnecessary toString call

 part of ONOS-7479

Change-Id: I859d89c425538dc7db36a177068b130b3052a784
diff --git a/model/src/main/java/org/onosproject/yang/model/LeafNode.java b/model/src/main/java/org/onosproject/yang/model/LeafNode.java
index 4f2f526..dca3cc0 100644
--- a/model/src/main/java/org/onosproject/yang/model/LeafNode.java
+++ b/model/src/main/java/org/onosproject/yang/model/LeafNode.java
@@ -82,7 +82,7 @@
                 "key=" + key() + ", " +
                 "value=" + asString() +
                 "valueNamespace=" + valueNamespace() +
-                "leafType=" + leafType.toString() +
+                "leafType=" + leafType +
                 "}";
     }