crypto: md5 - remove unused macros

crypto/md5.c:26:0: warning: macro "MD5_DIGEST_WORDS" is not used [-Wunused-macros]
crypto/md5.c:27:0: warning: macro "MD5_MESSAGE_BYTES" is not used [-Wunused-macros]

They are never used since commit 3c7eb3cc ("md5: remove from
lib and only live in crypto").

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>