The files it downloads are not versioned, and they could
change any time. GRUB has no way to deterministically grab
these.

I've removed GRUB's local for grabbing these, instead
mirroring them myself and checking hashes; no hashes seem
to have been provided by the upstream at Translation Project,
so I just used the hashes I had on the files it had, when
I downloaded them.

From now on, I can just re-download these and re-calculate
the hashes as desired, over time, when updating GRUB revisions.

Signed-off-by: Leah Rowe <leah@libreboot.org>

we have the "default" tree, then the "nvme" tree which adds
nvme support.

the "xhci" tree adds xhci patches, *and* nvme patches.

riku suggested that i rename it accordingly, and his advice
was quite correct, indeed wise.

this will reduce confusion for contributors, including *myself*.

Signed-off-by: Leah Rowe <leah@libreboot.org>