crypto: x86/serpent-sse2 - remove XTS algorithm

The XTS template now wraps an ECB mode algorithm rather than the block
cipher directly.  Therefore it is now redundant for crypto modules to
wrap their ECB code with generic XTS code themselves via xts_crypt().

Remove the xts-serpent-sse2 algorithm which did this.  Users who request
xts(serpent) and previously would have gotten xts-serpent-sse2 will now
get xts(ecb-serpent-sse2) instead, which is just as fast.

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