ath10k: remove debugfs support for Per STA total rx duration

cfg80211/nl80211 interface changes for per STA total rx-duration and
very basic 'ath10k_sta_statistics'  mac80211 callback is implemented
to extend support for per station statistics from the driver.

Also provision in 'iw dev wlan#N station dump' to parse rx-duration
is supported. So its safer to remove the debugfs entry for per STA
rx-duration

Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>