Remove type paramter bounds because Object is implicitly inherited

Change-Id: I7b933d924192d4b6bd079969cf4702d1c08f684f
diff --git a/core/api/src/main/java/org/onlab/onos/event/AbstractEvent.java b/core/api/src/main/java/org/onlab/onos/event/AbstractEvent.java
index 49fb268..e0717f1 100644
--- a/core/api/src/main/java/org/onlab/onos/event/AbstractEvent.java
+++ b/core/api/src/main/java/org/onlab/onos/event/AbstractEvent.java
@@ -22,7 +22,7 @@
 /**
  * Base event implementation.
  */
-public class AbstractEvent<T extends Enum, S extends Object> implements Event<T, S> {
+public class AbstractEvent<T extends Enum, S> implements Event<T, S> {
 
     private final long time;
     private final T type;