Unnecessary warning message for deletion.

Moved from ZBXNEXT-7951 21st sub issue.

Steps to reproduce:

1. Open /templates.php;
2. Press on "Import" button;
3. Import any template export file, which contains information, that will either add or update existing template;
4. Select all rules for import, including all checkboxes for "Delete missing";
5. Press the "Import" button;
6. Observe, that nothing was deleted, but warning about deleting all elements, that are not present is displayed.

Result:

Expected:
Such warning message not to be displayed, when nothing is deleted.