staging: r8188eu: remove unused cck, ofdm and mcs rate defines

Remove some unused defines for cck, ofdm and mcs rates.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20220110124638.6909-9-martin@kaiser.cx


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