Remove discovery configuration info in contrail-dns

* Since the discovery client has been removed from contrail-dns since
  89170cc, the discovery information in
  the file is no more needed.

Change-Id: I3f57103011b7db7450b5cc5520e146ea2d844ca3
Closes-Bug: #1677307

src/dns/contrail-dns.conf

@@ -35,10 +35,6 @@ log_local=1
 # second. System logs are dropped if the sending rate is exceeded
 # sandesh_send_rate_limit=
 
-[DISCOVERY]
-# port=5998
-# server=127.0.0.1 # discovery_server IP address
-
 [IFMAP]
 # certs_store=
 # password=dns-user-passwd