staging: r8188eu: remove usb_{read,write}_mem()

Remove usb_{read,write}_mem() because they are unused.

Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Co-developed-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Link: https://lore.kernel.org/r/20210917071837.10926-2-fmdefrancesco@gmail.com


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