Input: ixp4xx-beeper - delete driver

The NSLU2 has been migrated to devicetree and there we use
the gpio-beeper.c driver instead, the boardfile will be deleted
for kernel v5.15 so drop this custom and now unneeded driver.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20210714115028.916360-1-linus.walleij@linaro.org


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>