staging: r8188eu: clean up rtw_rf.c

Remove unnecessary includes and the unused define _RTW_RF_C_ from
rtw_rf.c.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20220222082847.6687-4-straube.linux@gmail.com


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