ath6kl: Remove few unused WMI stuff

* Removed unused WOW_MAX_FILTER_LISTS macro.

* Removed empty ath6kl_wmi_get_wow_list_event_rx() function.
  List of configured WOW patterns are maintained in CFG layer
  itself. No need to have this function in ath6kl to get
  configured WOW pattern list. It can added later if we need
  it for debugging.

Signed-off-by: Raja Mani <rmani@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>