wifi: rtl8xxxu: drop reference to staging drivers

The Kconfig notes mention staging drivers that have
since been removed so update the driver's description
so it no longer references the staging rtl8723au and
rtl8192u drivers which have now been deleted.

Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20240805221910.3765214-1-pbrobinson@gmail.com