ath9k_hw: Remove BTCOEX initvals

The MAX_TXPWR table for BTCOEX is not needed for AR9462.
Programming these values to the HW results in undesirable
behavior - for example, large number of delimiter/data
underruns are seen in AES-CCMP mode. Also, registers like
AR_PCU_MISC_MODE2 return 0xdeadbeef after the BTCOEX_MAX
power table is programmed to the HW, and frames being transmitted
end up being looped back to the RX engine, an example being beacon
frames in IBSS mode.

Remove this table for now - this fixes CCMP performance and general
IBSS usage.

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