ath10k: htc: removal of unused struct members

Removed tx_credits_per_max_message and tx_credit_size
from struct ath10k_htc_ep since they are not used
anywhere in the code.

They are just written, never read.

Signed-off-by: Erik Stromdahl <erik.stromdahl@gmail.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>