wifi: ath10k: drop HTT_DATA_TX_STATUS_DOWNLOAD_FAIL

According to Jeff, 'HTT_DATA_TX_STATUS_DOWNLOAD_FAIL' from
'enum htt_data_tx_status' is never actually used by the
firmware code and so may be dropped, with the related
adjustment to 'ath10k_htt_rx_tx_compl_ind()'.

Suggested-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>

Found by Linux Verification Center (linuxtesting.org) with SVACE.
Acked-by: Jeff Johnson <quic_jjohnson@quicinc.com>

Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20230914160744.155903-1-dmantipov@yandex.ru