Fix EZP-23348: Misleading error message on deleted embed objects

Link: https://jira.ez.no/browse/EZP-23348

## Description
When a deleted embed object is displayed the embed_denied.tpl template was used.
https://github.com/ezsystems/ezpublish-legacy/blob/master/design/standard/templates/content/datatype/view/ezxmltags/embed_denied.tpl
This could lead the user to think it was a permission issue.

This patch makes it display a more accurate error message.

## Tests
Manual tests