overlay.d/40grub: delete 30_console.cfg file

See coreos/fedora-coreos-tracker#1671
where we discovered that having this be a static config delivered
by bootupd was a bad idea.

Instead we'll have something else create a file in /boot/grub2/console.cfg
(most likely osbuild/osbuild#1589) and we'll have
the bootupd static grub configs source it (coreos/bootupd#619).