staging: rtl8188eu: remove unused macros

usb_ops_linux.h contains a couple of macros to make functions usable as
urb completion callbacks. Most of them are unused and can be removed.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20210407170531.29356-1-martin@kaiser.cx


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