Remove unused variants of Skein

[mcmilk]

The variants Skein-256 and Skein-1024 aren't used within OpenZFS.

Motivation and Context

Cleanup icp module - encryption and hashing.

Description

The code is public domain, so there is ne need for additional licensing information: THIRDPARTYLICENSE* removed, and CDDL headers added. Also the debugging and the two unused variants got removed.

How Has This Been Tested?

I compiled on FreeBSD and Linux machines.
No big endian machine currently :(

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[Low-power]

No big endian machine currently

It builds on my big-endian POWER7 machine, with Linux 4.1 and 6.1. No further testings are done because current running kernel can't be used to test zfs.ko.

[mcmilk]

No big endian machine currently

It builds on my big-endian POWER7 machine, with Linux 4.1 and 6.1. No further testings are done because current running kernel can't be used to test zfs.ko.

@Low-power - I have access to POWER8 and POWER9 OpenStack VMs - is there some ready to use FreeBSD 13.x Disk Image somewhere? I would like to setup an big endian FreeBSD buildbot then. Also one for ppc64le ... maybe I don't have to search a lot, when you can tell me some fast link ;-)

[Low-power]

Unfortunately I didn't have my hands on FreeBSD/powerpc64 right this time. I only experienced working FreeBSD/powerpc64 live system under QEMU/KVM, so I guess using the standard iso images should be fine.

[jumbi77]

@mcmilk Can you may rebase this? And is this blocked due to no-testing-capability for big endian systems? Can we may use buildbot or qemu for this?

[mcmilk]

I have FreeBSD and Linux POWER8, POWER9 and POWER10 machines now.
But the time is a bit limited. I will just rebase this first... and maybe test later on Big Endian also.