remove unnecessary clause from replication_manager:get_actual_replications

we will get [] from ns_vbm_sup:get_children since we know that ns_vbm_sup
was already started

Change-Id: Id14f84d107b1fd728911ef47fb0bffdffd67d37d
Reviewed-on: http://review.couchbase.org/38117
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>