beet remove --delete should NOT default to "yes"

```bash
beet remove --delete albumartist:'miles' album:'porgy'
...
Really DELETE 15 files? (Yes/no/select)
```

I pressed enter here and it deleted the files! Seems like if it's going to warn about a destructive action, it should also default to NO, not YES.

Start at the confirmation prompt used by `beet remove --delete` and reproduce the command shown in the issue. The change is done when pressing Enter keeps the files intact, while an explicit affirmative response still permits deletion; add or update coverage for this prompt behavior if the existing test location is found.

Written by the indexing model from the issue text.