crypto: des_s390: remove des3_ede128 mode

des_s390 implements support for 3DES with a 128 bit key. This mode is probably
not used anywhere, less secure than 3DES with a 192 bit key and not
implemented in the generic des version. Removing this mode seems to be low risk
and will ease maintenance of the code.

Signed-off-by: Jan Glauber <jang@linux.vnet.ibm.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>