net: remove references to CONFIG_IRDA in network header files

Commit d64c2a76

 ("staging: irda: remove the irda network stack and
drivers") removes the config IRDA.

Remove the remaining references to this non-existing config in the network
header files.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20211229113620.19368-1-lukas.bulwahn@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>