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

@@ -1,10 +1,15 @@
 rec {
+  users = import ./users.nix;
+
+  adminSSHKeys = builtins.concatLists (
+    map (user: getSSHKeys user.name) (
+      builtins.filter (user: user.value.admin or false) (attrsToList users)
+    )
+  );
+
   attrsToList = mapAttrsToList nameValuePair;
-
   mapAttrsToList = f: attrs: builtins.attrValues (builtins.mapAttrs f attrs);
-
   nameValuePair = name: value: { inherit name value; };
-
   toList = x: if builtins.isList x then x else [ x ];
 
   getSSHKeys =
@@ -13,12 +18,4 @@ rec {
       toList users.${username}.ssh
     else
       builtins.warn "user ${username} declared without ssh keys" [ ];
-
-  users = import ./users.nix;
-
-  adminSSHKeys = builtins.concatLists (
-    map (user: getSSHKeys user.name) (
-      builtins.filter (user: user.value.admin or false) (attrsToList users)
-    )
-  );
 }