Registration editing submission confirmation

One-sentence description

Misleading confirmation message after editing submission of a registered event.

Current behaviour

The submission editing was completed with the message "you successfully cancelled the registration".

Expected behaviour

The submission editing should complete with a message indicating the success of editing.

Steps to reproduce

1. Go to the symposium event page https://thalia.nu/events/237/.
2. Press the button "edit submission".
3. Fill in symposium preferences.
4. Save preferences. Now the green bar at the top of the page shows the above success message.

Note I did this previous weekend, so the button descriptions may vary.