Deleting an import task results in imported data being deleted without confirmation

[TjerkNan]

Describe the bug
Deleting an import from the list of imports also deletes the imported data.
I've confirmed this because when a RIS file is imported twice, a duplicate is detected.
However, if the imports are then deleted, and the test RIS file is imported again, no duplicate is detected.

If data is deleted from the database, I would expect a confirmation dialog.

To Reproduce
Steps to reproduce the behavior:

1. Import a RIS file
2. Delete the import
3. observe no confirmation

Expected behavior
A confirmation before deletion.