staging: rtl8188eu: Remove function nat25_db_expire()

We've removed the code which was responsible for building NAT table,
so no use of keeping nat_db_expire().

Signed-off-by: navin patidar <navin.patidar@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --cc drivers/staging/rtl8188eu/core/rtw_mlme.c
Simple merge

diff --cc drivers/staging/rtl8188eu/include/usb_osintf.h
Simple merge