wifi: brcmsmac: cleanup SCB-related data types

Drop unused and set-but-unused fields of 'struct scb_ampdu_tid_ini',
'struct scb_ampdu' and 'struct scb', as well as now unused argument
of 'brcms_c_ampdu_tx_operational()', adjust related code.

Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230725162400.192357-2-dmantipov@yandex.ru