Revert "tree-wide: replace xscreensaver with xsecurelock"

This reverts commit 06f6e59fc9.

nix/configurations/vanadium/nixos/gui.nix

@@ -41,6 +41,16 @@
     };
   };
 
+  services.xscreensaver = {
+    enable = true;
+    hooks = {
+      # Reset display setting on login
+      "RUN" = ''
+        ${lib.getExe pkgs.autorandr} --change --ignore-lid
+      '';
+    };
+  };
+
   services.picom = {
     enable = true;
     # avoid tearing

nix/configurations/vanadium/nixos/locale.nix

@@ -29,6 +29,7 @@
       let
         genLocale = locale: lib.flip lib.genAttrs (_: locale);
       in
+      # - xscreensaver freaks out on the time display
       # - evolution add event becomes hard to use
       #   https://gitlab.gnome.org/GNOME/evolution/-/issues/3120
       genLocale "fr_FR.UTF-8" [