Remove duplicate registration.

- Should fix following warnings:
 (no name): long already registed as 7. Skipping 326.
 (no name): class org.onlab.packet.Ip4Address already registed as 70. Skipping 327.

Change-Id: I5a3ee1a219b567617f964ddaca16b0cc9dcef5ea

@@ -76,10 +76,8 @@ public class DistributedDhcpStore implements DhcpStore {
                                 .register(KryoNamespaces.API)
                                 .register(IpAssignment.class,
                                         IpAssignment.AssignmentStatus.class,
-                                        Date.class,
-                                        long.class,
-                                        Ip4Address.class)
-                                .build()))
+                                        Date.class)
+                                .build("dhcp")))
                 .build();
 
         freeIPPool = storageService.<Ip4Address>setBuilder()