wifi: ath12k: remove the unused scan_events from ath12k_wmi_scan_req_arg

As done for ath11k, lets keep on cleaning up struct ath12k_wmi_scan_req_arg by
removing the unused scan_events. Also remove the underlying union & struct
construct as it isn't needed anymore. No functionnal changes.

Signed-off-by: Nicolas Escande <nico.escande@gmail.com>
Acked-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://msgid.link/20240211151104.1951418-1-nico.escande@gmail.com