Completion with Vimwiki omnicompletion function

- [X] I have fzf 0.23.0 or above
- [x] I have read through https://github.com/junegunn/fzf.vim/blob/master/README.md
- [x] I have read through https://github.com/junegunn/fzf/blob/master/README-VIM.md
- [x] I have read through the manual page of fzf (`man fzf`)
- [x] I have searched through the existing issues

I'm trying to setup a shortcut to use Vimwiki's omnicompletion in combination with fzf, but I fail to see how to do this exactly.

In the issues I found #1221. This works with other completion methods such as file completion but with omni-completion it doesn't seem to work. When I type for example `[[meetings` followed by `` fzf simply inserts some text into the buffer:

```
[[meetings/1207:call 175_complete_trigger()
```

I also tried with the following in my vimrc:

```vim
inoremap fzf#vim#complete('Complete_wikifiles')
```

But this has the exact same effect when typing `[[meetings` and pressing ``.

Has anyone done something similar before?

The Vimwiki omnifunc can be found here: https://github.com/vimwiki/vimwiki/blob/dev/ftplugin/vimwiki.vim#L24