The SM2 algorithm has a single user in the kernel. However, it's
never been integrated properly with that user: asymmetric_keys.
The crux of the issue is that the way it computes its digest with
sm3 does not fit into the architecture of asymmetric_keys. As no
solution has been proposed, remove this algorithm.
It can be resubmitted when it is integrated properly into the
asymmetric_keys subsystem.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>