ath10k: remove sw encryption for pmf

Software encryption was never necessary.
Tested with fw 636 and fw 10.x.

Signed-off-by: Marek Kwaczynski <marek.kwaczynski@tieto.com>
Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>