Staging: rtl8723au: Remove unused functions and prototype

The functions rtw_ap_inform_ch_switch23a, rtw_acl_remove_sta23a and
rtw_acl_add_sta23a are not used anywhere in the kernel. So remove their
definition and prototype.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>