ath9k: Cleanup IQ calibration for PCOEM chips

Since IQ calibration is done as part of AGC calibration for
AR9485 and above, remove the seperate IQ calibration code.

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