Crm 12741 fix

when a price set is configured for a event or contribution, and if we try deleting it, it does not get deleted and throws a messge to user showing the entities (event / contribution) attached to it in proper format with links for editing the fee / amount section of it.

the issue : 
if a price set is used for a event template, and that is being deleted by user, no message is shown to user, and civi attempts to delete the price set which throws a DB contraint violation error as civicrm_price_set_entity foreign key is linked to that price set.

handled civicrm_event_template while price set getting deleted just like as event or contribution and a proper message is shown to user.