Delete duplicated kubernates namespace config entry

etc/emqx.conf

@@ -158,12 +158,6 @@ cluster.autoclean = 5m
 ## Value: String
 ## cluster.k8s.namespace = default
 
-## Kubernates Namespace
-##
-## Value: String
-## cluster.k8s.namespace = default
-
-
 ##--------------------------------------------------------------------
 ## Node
 ##--------------------------------------------------------------------