As you know, there are no dialogs in Instant Web Publishing, so when you delete a record using a script, you don't really get a warning: with the status bar hidden, you don't even get a submit or cancel button. Accordingly we have not enabled deletion in the IWP Module. (The module was designed as a companion to the traditional FileMaker client, not a replacement for it, so we suggest folks delete records only in the regular version of the calendar using FileMaker Pro.)
Should you wish to enable deletion in your copy of the IWP module, you might consider doing so from a layout where the status area is visible as this gives you some confirmation of the deletion. You can also send the user a delete confirmation message on a new layout that presents a continue or cancel option for the deletion.