staging: r8188eu: remove function rtw_hal_free_xmit_priv

Remove function rtw_hal_free_xmit_priv in hal/hal_intf.c and its
declaration in include/hal_intf.h, as well as the single call line in
core/rtw_xmit.c. This function now essentially checks a function
pointer which will always be NULL (due to previous patches) and
therefore will never be called.

Acked-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
Link: https://lore.kernel.org/r/20210818234253.208271-6-phil@philpotter.co.uk


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>