s390: Remove arch_has_random, arch_has_random_seed

These symbols are currently part of the generic archrandom.h
interface, but are currently unused and can be removed.

Signed-off-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20200110145422.49141-4-broonie@kernel.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>