staging: r8188eu: remove unused HW_VAR_RF_TYPE

After previous cleanups HW_VAR_RF_TYPE is unused now.
Remove it.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20211128170924.5874-9-straube.linux@gmail.com


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