11746 fix delete custom field (#12092)

* 11746 delete custom field

* 11746 use filter instead of exclude

netbox/extras/models/customfields.py

@@ -215,7 +215,7 @@ class CustomField(CloningMixin, ExportTemplatesMixin, WebhooksMixin, ChangeLogge
         """
         for ct in content_types:
             model = ct.model_class()
-            instances = model.objects.filter(**{f'custom_field_data__{self.name}__isnull': False})
+            instances = model.objects.filter(custom_field_data__has_key=self.name)
             for instance in instances:
                 del instance.custom_field_data[self.name]
             model.objects.bulk_update(instances, ['custom_field_data'], batch_size=100)