emacs: Ignore the magical XF86WakeUp keysym.

For some reason, the `Fn' key on crybaby generates this keysym.  Having
Emacs feep when I bounce on it is annoying, since it ought to be a
perfectly innocent modifier key.

I've bound the key to an empty string, since this acts as a keyboard
macro and does nothing.  No other particularly simple binding seems to
work (`nil' and `undefined' continue to feep; and there's no obvious
do-nothing function to bind to the key).