remove support for sockets in pseudofiles

(1) we can't make them on a real filesystem except by running
something that calls socket()
(2) whyever would we want to?

modules/s6/default.nix

@@ -41,7 +41,6 @@ let
     s6-linux-init-shutdownd = dir {
       fifo = {
         type = "i";
-        subtype = "f";
         mode = "0600";
       };
       run = {
@@ -55,7 +54,6 @@ let
     s6-svscan-log = dir {
       fifo = {
         type = "i";
-        subtype = "f";
         mode = "0600";
       };
       notification-fd = { file = "3"; };