appletalk: remove ipddp driver

After the cops driver is removed, ipddp is now the only
CONFIG_DEV_APPLETALK but as far as I can tell, this also has no users
and can be removed, making appletalk support purely based on ethertalk,
using ethernet hardware.

Link: https://lore.kernel.org/netdev/e490dd0c-a65d-4acf-89c6-c06cb48ec880@app.fastmail.com/
Link: https://lore.kernel.org/netdev/9cac4fbd-9557-b0b8-54fa-93f0290a6fb8@schmorgal.com/
Cc: Doug Brown <doug@schmorgal.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20231009141139.1766345-1-arnd@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>