Staging: rtl8723au: Remove unused function rtw_atimdone_event_callback23a

This patch fixes the following sparse warning:

warning: symbol 'rtw_atimdone_event_callback23a' was not declared.
Should it be static?
rtw_atimdone_event_callback23a is local to the file rtw_mlme.c but
it isn't exposed in a header file anywhere. Moreover it is never called
from anywhere as well.

So, this patch removes this function completely.

Signed-off-by: Somya Anand <somyaanand214@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>