ath5k: remove unused and write-only structures and fields

struct ath5k_avg_val is unused.

In struct ath5k_hw, lladdr, ah_radar and ah_mac_revision are write-only,
rxbufsize is unused, ah_phy is write-only and referenced by unused
macros.

In struct ath5k_vif, lladdr is write-only.

Remove AR5K_TUNE_RADAR_ALERT, which has no effect.

Signed-off-by: Pavel Roskin <proski@gnu.org>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Acked-by: Nick Kossifidis <mickflemm@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>