linux/random.h: Remove arch_has_random, arch_has_random_seed

The arm64 version of archrandom.h will need to be able to test for
support and read the random number without preemption, so a separate
query predicate is not practical.

Since this part of the generic interface is unused, remove it.

Signed-off-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20200110145422.49141-5-broonie@kernel.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>