[Toybox] Microsoft github took down the xz repo.

[Rob Landley]

FYI, Microsoft Github disabled the xz repository because it became
"controversial" (I.E. there was an exploit in the news).

  https://social.coop/@eb/112182149429056593

  https://github.com/tukaani-project/xz

I'm assuming if toybox ever has a significant bug, microsoft would respond by
deleting the toybox repository. There's a reason that I have
https://landley.net/toybox/git on my website, and my send.sh script pushes to
that _before_ pushing to microsoft github.

Luckily the xz guys don't seem to trust microsoft github either, because the
upstream of the xz-embedded repo with the public domain code I cloned is:

  https://git.tukaani.org/xz-embedded.git

Which is still available.

Rob