Hi Mikko,
In custom screens you can choose to include or remove whatever functionality that suits your need.
The delete button has not been removed by default, so I would recommend that you ask the customer if they want the functionality enabled. And as it is only available for administrators (by default) I would recommend adding it again.
In the form page of the screen, this is the code:
HtmlElement formPage = addHtmlElement(getScreenElementId(screenElementIndex),
getScreenElementName(screenElementIndex),
getScreenElementType(screenElementIndex),
getScreenElementConfig(screenElementIndex));
if (ticketId > 0 &&
ticket.getValue("status") != "4" &&
getActiveUser().isAdministrator() &&
getCgiVariable("actionType").toInteger() == 2)
{
formPage.setFieldValue("addButton", Map().insert("name", "delete").insert("label", getLanguageVariable("delete")).insert("warning", getLanguageVariable("sureDelete")).insert("style", "red"));
}