staging: r8188eu: remove unused constants and variables

Remove some unused constants and variables that are left over from
previous cleanup patches.

Suggested-by: Martin Kaiser <martin@kaiser.cx>
Acked-by: Martin Kaiser <martin@kaiser.cx>
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20211017111705.18989-1-straube.linux@gmail.com


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