bug#55427: emacs-libgit tests are broken

[Kyle Meyer]

Zhu Zihao writes:

> Due to the inactive status of upstream. I'm planning to remove the
> emacs-libgit input of emacs-magit.
>
> magit will still work with the git executable if there's no
> emacs-libgit.
>
> Any thoughts?

Good idea.  There's no real downside to disabling libgit2 support
because magit-libgit.el does very little at this point.