MFC r336084-r336085, r336118: Move zfs impl into libsa

r336084:
Move ZFS files into libsa

Move the libzfs stuff into libsa. There's no need for it to be a
separate library. The separate library adds to the issues of build
ordering that we see from time to time. Move the filesystem support
into libsa, like all the other filesystem support rather than making
zfs the odd-duck out.

Discussed with: allanjude@

r336085:
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.

r336118:
Remove dirs that git svn should have removed but didn't.