simplify "symlink name stack"

simplify "symlink name stack"

With well defined and kernel-supplied node names, we no longer need
to support a possible stack of conflicting symlinks and node names.
Only symlinks with identical names can be claimed by multiple devices.

This shrinks the former /dev/.udev/names/ significantly.

Also the /dev/{block,char}/MAJ:MIN" links are excluded from the name
stack - they are unique and can not conflict.