random: kill random_harvestq_cache

Function intended to load entropy from a cache file.
Code needed for random_harvestq_cache isn't even on tree, it's not
being compiled, neither is intended to be used in the future AFAIC,
so let's kill it.

Signed-off-by: Raphael S. Carvalho <raphaelsc@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>