crypto: ahash - remove crypto_ahash_alignmask

crypto_ahash_alignmask() no longer has any callers, and it always
returns 0 now that neither ahash nor shash algorithms support nonzero
alignmasks anymore.  Therefore, remove it.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>