ath9k: Remove MAC_DEBUG

This option has not been enabled by default in any
distribution, has never been enabled in OpenWrt and no developer
has asked for this information in a bug report.

Dumping pages of random values doesn't help debugging,
remove this option (along with the vmalloc() abuse).

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