ath9k_htc: Remove interface combination specific checks

Once the driver advertizes interface combination logic
based on its firmware/hardware limitation, cfg80211
takes care of all the necessary logic such as maximum
beaconing vifs, standlone interface etc.

Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>