Remove duplicated option

Change-Id: I38e594c5e60baaa813bcfd8623aca9547d886754
diff --git a/oslo_templates/files/queens/oslo/messaging/_rabbit.conf b/oslo_templates/files/queens/oslo/messaging/_rabbit.conf
index f56e97d..3a12be1 100644
--- a/oslo_templates/files/queens/oslo/messaging/_rabbit.conf
+++ b/oslo_templates/files/queens/oslo/messaging/_rabbit.conf
@@ -177,7 +177,6 @@
 # server processes hog all the messages leaving others out of business.
 # That leads to artificial high message processing latency and at the
 # extrime to MessagingTimeout errors.
-rabbit_qos_prefetch_count = 64
 rabbit_qos_prefetch_count = {{ _data.get('rabbit_qos_prefetch_count', 64) }}
 
 # Number of seconds after which the Rabbit broker is considered down