powerpc: Drop Open Hack'Ware

powerpc: Drop Open Hack'Ware

Open Hack'Ware was an alternative firmware of powerpc under QEMU.

The last commit to any Open Hack'Ware repo I can find is from 2014 [1].

Open Hack'Ware was used for the QEMU "prep" machine type, which was
deprecated in QEMU in commit 54c86f5a4844 (hw/ppc: deprecate the
machine type 'prep', replaced by '40p') in QEMU v3.1, and had reportedly
been broken for years before without anyone noticing. Support was removed
in February 2020 by commit b2ce76a0730e (hw/ppc/prep: Remove the
deprecated "prep" machine and the OpenHackware BIOS).

Open Hack'Ware's limitations require some messy code in GRUB. This
complexity is not worth carrying any more.

Remove detection of Open Hack'Ware. We will clean up the feature flags
in following commits.

[1]: https://github.com/qemu/openhackware and
     https://repo.or.cz/w/openhackware.git are QEMU submodules. They have
     only small changes on top of OHW v0.4.1, which was imported into
     QEMU SCM in 2010. I can't find anything resembling an official repo
     any more.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>