ath10k: htt: remove array of flexible structures

I updated to sparse v0.6.4 and it warns:

drivers/net/wireless/ath/ath10k/hw.c: note: in included file (through drivers/net/wireless/ath/ath10k/core.h):
drivers/net/wireless/ath/ath10k/htt.h:1503:41: warning: array of flexible structures
drivers/net/wireless/ath/ath10k/htt_rx.c: note: in included file (through drivers/net/wireless/ath/ath10k/core.h):
drivers/net/wireless/ath/ath10k/htt.h:1503:41: warning: array of flexible structures

The structure is unused in ath10k so let's just remove it.

Compile tested only.

Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20211209091545.6098-1-kvalo@kernel.org