mac802154: remove aack hw flag

This patch removes the hardware auto acknowdledge flag which indicates
that the transceiver supports this handling. This flag is never
evaluated inside mac802154 and all transceivers should support this
handling by default per hardware.

Suggested-by: Lennert Buytenhek <buytenh@wantstofly.org>
Cc: Alan Ott <alan@signal11.us>
Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Reviewed-by: Varka Bhadram <varkabhadram@gmail.com>
Acked-by: Stefan Schmidt <stefan@osg.samsung.com>
Acked-by: Varka Bhadram <varkabhadram@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>