ath9k: Remove remaining occurrences of CONFIG_SLOW_ANT_DIV

Slow Antenna Diversity has been removed, these are remnants
of the old code.

Signed-off-by: Sujith <Sujith.Manoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

diff --cc drivers/net/wireless/ath9k/core.h
Simple merge

diff --cc drivers/net/wireless/ath9k/hw.c
Simple merge

diff --cc drivers/net/wireless/ath9k/main.c
Simple merge