staging: r8188eu: remove rtw_hal_c2h_handler function

staging: r8188eu: remove rtw_hal_c2h_handler function

Remove rtw_hal_c2h_handler function from hal/hal_intf.c, as well as its
declaration in include/hal_intf.h, and remove its one remaining caller
within core/rtw_cmd.c.

This function was a wrapper function, then simplified to always return
_FAIL. Since it has no further use, remove it, as part of ongoing
efforts to simplify and remove the HAL layer of the driver.

Acked-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Acked-by: Michael Straube <straube.linux@gmail.com>
Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
Link: https://lore.kernel.org/r/20210829234541.946-4-phil@philpotter.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>