staging: r8188eu: remove lines from Makefile that silence build warnings

Remove the several lines from the Makefile that append EXTRA_CFLAGS options
to silence build warnings about unused variables, unused functions and such
like. This will enable cleanup of missed warnings, and easier spotting
of future such problems.

Acked-by: Michael Straube <straube.linux@gmail.com>
Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
Link: https://lore.kernel.org/r/20210810235047.177883-9-phil@philpotter.co.uk


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