staging: r8188eu: remove unused function RT_usb_endpoint_is_bulk_in

Remove the RT_usb_endpoint_is_bulk_in function which is not used.

RT_usb_endpoint_dir_in is no longer used either and can also be removed.

Acked-by: Michael Straube <straube.linux@gmail.com>
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20210910202151.4007-3-martin@kaiser.cx


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