Revert "ath9k: export HW random number generator"

This reverts commit 6301566e

. Oleksij Rempel
noticed that the randomness doesn't look to be good enough and Stephan Mueller
commented:

"I would say that the discussed RNG does not seem fit for hooking it up with the
hwrandom framework."

http://lkml.kernel.org/g/3945775.m5HblJPgiO@tauon.atsec.com

So let's the revert the patch until we are sure that we can trust this random
generator.

Signed-off-by: Kalle Valo <kvalo@codeaurora.org>