Remove undefined variable

$SUBID is not defined in this steps. So, we get following error when we run the commands as is.
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$ az network route-table route create -g $RG --name $FWROUTE_NAME --route-table-name $FWROUTE_TABLE_NAME --address-prefix 0.0.0.0/0 --next-hop-type VirtualAppliance --next-hop-ip-address $FWPRIVATE_IP --subscription $SUBID
argument --subscription: expected one argument
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Author: Jumpei Yamashita

articles/aks/limit-egress-traffic.md

@@ -378,7 +378,7 @@ Create an empty route table to be associated with a given subnet. The route tabl
 # Create UDR and add a route for Azure Firewall
 
 az network route-table create -g $RG -l $LOC --name $FWROUTE_TABLE_NAME
-az network route-table route create -g $RG --name $FWROUTE_NAME --route-table-name $FWROUTE_TABLE_NAME --address-prefix 0.0.0.0/0 --next-hop-type VirtualAppliance --next-hop-ip-address $FWPRIVATE_IP --subscription $SUBID
+az network route-table route create -g $RG --name $FWROUTE_NAME --route-table-name $FWROUTE_TABLE_NAME --address-prefix 0.0.0.0/0 --next-hop-type VirtualAppliance --next-hop-ip-address $FWPRIVATE_IP
 az network route-table route create -g $RG --name $FWROUTE_NAME_INTERNET --route-table-name $FWROUTE_TABLE_NAME --address-prefix $FWPUBLIC_IP/32 --next-hop-type Internet
 ```