opencrypto: Nix CRYPTO_F_USER, CRYPTO_F_CBIMM, CRYPTO_F_CBIFSYNC.

CRYPTO_F_USER is no longer needed.  It was introduced in 2008 by
darran@ in crypto.c 1.30, cryptodev.c 1.45 in an attempt to avoid
double-free between the issuing thread and asynchronous callback.
But the `fix' didn't work.  In 2017, knakahara@ fixed it properly in
cryptodev.c 1.87 by distinguishing `the crypto operation has
completed' (CRYPTO_F_DONE) from `the callback is done touching the
crp object' (CRYPTO_F_DQRETQ, now renamed to CRYPTODEV_F_RET).

CRYPTO_F_CBIMM formerly served to invoke the callback synchronously
from the driver's interrupt completion routine, to reduce contention
on what was once a single cryptoret thread.  Now, there is a per-CPU
queue and softint for much cheaper processing, so there is less
motivation for this in the first place.  So let's remove the
complicated logic.  This means the callbacks never run in hard
interrupt context, which means we don't need to worry about recursion
into crypto_dispatch in hard interrupt context.

(riastradh)