staging: r8188eu: remove unused IEEE_* defines

The IEEE_* defines in the driver's ieee80211.h header file are not used.
Remove them.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20220502200652.143665-10-martin@kaiser.cx


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