ath9k_hw: merge ath9k_hw_ani_monitor_old and ath9k_hw_ani_monitor_new

After the last rounds of cleanup, these functions are now functionally
equivalent and can thus be merged.
Also get rid of some excessive (and redundant) debug messages.

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