staging: r8188eu: remove the RT_TRACE macro

We've deleted all RT_TRACE calls. The macro itself can now be removed
as well.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20210807153636.11712-13-martin@kaiser.cx


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