Tested in 7.0-1, 7.0-5, 7.0-8 and 7.0-12

Steps to reproduce: 

1. Export a template as a YAML, XLM or JSON file
2. Add a Discovery rule of type Dependent item, the Master item being an item of the template.
3. Add a Discovery rule Filter to the same template via Web interface
4. Import back the previously exported template file via Web interface
5. Make sure `Discovery rules` `Delete missing` is checked, click `Import`
6. Observe that the newly added filter is marked to be deleted, click `Import`
7. Observe `Imported successfully`

Result:

The template's discovery rule filter is still present event though the web interface confirmed the deletion. The filter needs to be manually deleted.

Expected:

The template's discovery rule filter should have been deleted, as indicated by the import diff window, or an error should be displayed if this deletion is not possible this way.