Input: aiptek - remove double define

Constant AIPTEK_TOOL_BUTTON_PEN_MODE was defined twice.

Signed-off-by: Edwin van Vliet <edwin@cheatah.nl>
Reviewed-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>