Remove the duplicate items in the list

In the list like this:

```
1 /home/daniel/.config/fish/fundle/tuvistavie/fish-fastdir
2 /home/daniel
3 /home/daniel/Dropbox
4 /home/daniel/Dropbox/tmp
5 /usr/local
6 /home/daniel
7 /home/daniel/Dropbox
```

there are duplicates, and how can I make all the items unique? Specifically, remove all the old items like 2 and 3 and leave only the new one, of course the numbers in front of the items will be reordered.

The issue provides sample output from fish-fastdir but names no source file, test, or command entry point. Start by locating the code that produces the directory list; done means duplicate paths retain only the newest entry, the remaining numbers are consecutive, and the shown repeated paths are covered by a regression check.

Written by the indexing model from the issue text.