crypto: chacha20 - Remove cra_alignmask

Now that crypto_chacha20_setkey() and crypto_chacha20_init() use the
unaligned access macros and crypto_xor() also accepts unaligned buffers,
there is no need to have a cra_alignmask set for chacha20-generic.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>