When an item is not a composite item it will have a sort order of 0 therefore the below evaluation can be used to only display an item if it is the composite parent item.

FOREACH(OrderItems){BEGIN}EVAL<IIF["[{ORDERITEMS.COMPSORTORDER}]"="0","[{ORDERITEMS.ITEMNUMBER}] - [{ORDERITEMS.ITEMTITLE}] x [{ORDERITEMS.NQTY}]",""]> {END}

You need to use this tag in Settings > Email Notifications - double-click on the Despatch Notification Email then paste the above code into the template.