kernfs: remove static node creation, and update the text
This is to match the "new" way of device handling with devtmpfs (already
widely used in recent ten years).
In a normal booting process, the kernel mounts devtmpfs at very early
stage. So the static nodes won't be used at all. The only situation
where the kernel can't mount devtmpfs is "/dev is missing", but it means
those two static nodes can't exist anyway, and a normal LFS system
(without initramfs) won't boot in such a bad situation.
Removing static /dev/console and /dev/null may cause trouble for those
people or scripts chroot into LFS tree without mounting devtmpfs. But
entering a chroot with only console and null in /dev is already
problematic. For a reference, If a systemd service is started with
PrivateDevices=true, systemd will create 18 nodes and symlinks to form a
"minimal" /dev.
