libsa: Remove redundant sys/cdefs.h

Sponsored by: Netflix

Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

loader: zfs_cmd.c does not really compile without libzfs.h

Having libzfs.h wrapped in LOADER_ZFS_SUPPORT check does not really make sense,
because we do need function declarations with C99.

Sponsored by: Netflix, Klara Inc.

Regularize my copyright notice

o Remove All Rights Reserved from my notices
o imp@FreeBSD.org everywhere
o regularize punctiation, eliminate date ranges
o Make sure that it's clear that I don't claim All Rights reserved by listing
All Rights Reserved on same line as other copyright holders (but not
me). Other such holders are also listed last where it's clear.

Stop using ../zfs/libzfs.h but instead use libzfs.h.

While ../zfs/libzfs.h mostly works, there are a few situations where
it does not. Eliminate the problem by using plain libzfs.h, like we do
for ufs support. This fixes the weird cases, and is easier to
understand. It also follows the general style convetion of avoiding
../ in #includes.

Use M. Warner Losh everywhere on my copyrights.
Remove 'All Rights Reserved' where I can.

Consolidate three copies of ZFS commands into a central location.

There's no reason to have multiple copies of lszfs and
reloadbe. Consolidate them into one location. Also ldi_get_size is the
same everywhere (except sparc64). Make it the same everywhere as the
common definition is more general and will work on spar64.