crypto: rmd320 - remove rmd320 in Makefile

Commit 93f64202 ("crypto: rmd320 - remove RIPE-MD 320 hash algorithm")
removes the Kconfig and code, but misses to adjust the Makefile.

Hence, ./scripts/checkkconfigsymbols.py warns:

CRYPTO_RMD320
Referencing files: crypto/Makefile

Remove the missing piece of this code removal.

Fixes: 93f64202 ("crypto: rmd320 - remove RIPE-MD 320 hash algorithm")
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>