wifi: ath11k: Remove redundant ath11k_mac_drain_tx

ath11k_mac_drain_tx is already called in ath11k_mac_wait_tx_complete, no need to call it again. So remove it.

This is found in code review.

Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3

Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20220919020259.1746-1-quic_bqiang@quicinc.com