nixos/networking: fix extraHosts generation

The SSH host key files are already defined in the OpenSSH module, so
there is no need to persist them with impermanence.nix.

lib/default.nix

@@ -1,11 +1,11 @@
 rec {
-  toList = x: if builtins.isList x then x else [ x ];
-
-  nameValuePair = name: value: { inherit name value; };
+  attrsToList = mapAttrsToList nameValuePair;
 
   mapAttrsToList = f: attrs: builtins.attrValues (builtins.mapAttrs f attrs);
 
-  attrsToList = mapAttrsToList nameValuePair;
+  nameValuePair = name: value: { inherit name value; };
+
+  toList = x: if builtins.isList x then x else [ x ];
 
   getSSHKeys =
     username: