[BUG] Deleting a draft tiddler should not also delete the original tiddler

Describe the bug
Deleting a draft tiddler also deletes the associated original tiddler.

The original idea was that the delete operation should only be available in edit mode so as to reduce the change of accidental deletions while reading a wiki, and thus the need to delete the original tiddler as well as the draft. However, it turns out that draft tiddlers often get abandoned by users, and need to be cleaned up later. The fact that deleting such drafts also deletes the original tiddler does not match the users expectations.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://tiddlywiki.com/empty.html
2. Click the "new tiddler" button to create a new tiddler
3. Type some text in the body of the tiddler
4. Click the "tick" button to save the tiddler
5. Click the "edit" button to edit the new tiddler
6. Click the "delete" button to delete the draft tiddler
7. Click "OK" on the confirmation alert
8. Search for "New" to verify that the newly created tiddler has been deleted as well as its draft.

Expected behavior
Deleting a draft tiddler should not delete the associated original tiddler.

Reproduce the behavior in https://tiddlywiki.com/empty.html using the listed steps, then trace the delete action for a draft tiddler and its associated original. Done means deleting the draft removes only the draft, while the original tiddler remains available.