staging: rtl8723au: remove unimplemented function declarations

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Acked-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Cc: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>