staging: rtl8188eu: remove "rtw_ieee80211_back_parties"

This enum is unused. It is also close to "ieee80211_back_parties" in
"include/linux/ieee80211.h", which should be used if needed.

So remove it

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/f389e0d54a5a8a46c9a696207541aa1cb433676b.1624132543.git.christophe.jaillet@wanadoo.fr


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