libzfs_crypto.c doesn't need to use libkmf.h or pkcs11_random()

Review Request #2260 — Created Aug. 23, 2019 and submitted — Latest diff uploaded

11613, 11614

A few simplifications to libzfs_crypto as decribed in their bugs

Built illumos-gate (to verify the removal of libkmf.h was correct), the booted and ran the resuilting BE and created a few dummy zfs filesystems in a temporary zpool w/ encryption w/ a passphrase key (to verify the PBKDF2 code ran w/ the arc4random_buf change). I also peeked at the salt value to derive_key() to make sure that it was different each time I created an encrypted filesystem.