Issue #6140 - SelectorManager total keys.

Removed toString() override that was not calling super, to restore printing the total number of keys in dumps.

Signed-off-by: Simone Bordet <simone.bordet@gmail.com>

jetty-core/jetty-server/src/main/java/org/eclipse/jetty/server/ServerConnector.java

@@ -634,11 +634,5 @@ public class ServerConnector extends AbstractNetworkConnector
             onEndPointClosed(endpoint);
             super.endPointClosed(endpoint);
         }
-
-        @Override
-        public String toString()
-        {
-            return String.format("SelectorManager@%s", ServerConnector.this);
-        }
     }
 }