This reverts commit a3331eb87b.
See https://github.com/NixOS/nixpkgs/issues/2559#issuecomment-47313334
for a description why this is not a good idea.
I guess it's better to implement a sane way to remove all files in
authorized_keys.d, especially because it is also backwards-compatible.
Reopens#2559.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
da32f052b1