Rewrite the Device files section

Rewrite the Device files section

Remove the requirement to call MAKEDEV and prohibit attempting to
create or remove device files if a dynamic management facility is in
place.  Packages should assume device files in /dev are dynamically
managed.  Point people towards dynamic creation of named pipes and
document that creation in postinst is not the usual approach.  Extend
that discussion to device files outside of /dev, which are required
for some chroot or file system namespace approaches.

Remove the reference to old serial devices, which are now so old that
it's highly unlikely anyone will care.