ath9k_hw: remove ANI function restrictions for AP mode

The primary purpose of this piece of code was to selectively disable
OFDM weak signal detection. The checks for this are elsewhere, and an
earlier commit relaxed the restrictions for older chips, which are more
sensitive to interference.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>