staging: r8188eu: remove unused enum _NIC_VERSION

None of these enumerated values were used anywhere in the driver, so
just remove them all.

Link: https://lore.kernel.org/r/20210730092417.1014392-9-gregkh@linuxfoundation.org


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