The Alt+Numpad buffer that's maintained by the input stack is getting
corrupted, leading to garbage characters being inserted on keystrokes
like Alt+Up. Disable the automatic handling of Alt+Numpad for now until
the cause of this corruption is understood. The Alt+Numpad input did not
work anyway, so this does not regress anything.

Release Notes:

- windows: Fixed corrupted characters being inserted when Alt is pressed
(preview only)