wifi: rtlwifi: drop fill_fake_txdesc() from HAL interface

Since 'fill_fake_txdesc()' is actually implemented for rtl8192cu
only but never used, there is no need to maintain function pointer
in 'struct rtl_hal_ops' and 'rtl92cu_fill_fake_txdesc()' may be
dropped. Compile tested only.

Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20231016135925.129223-2-dmantipov@yandex.ru