chore: remove baked SSH key from template user

Rely on cloud-init SSH key injection from secrets for access rotation instead of storing an authorized key in the template config.

nixos/template-base/configuration.nix

@@ -30,9 +30,6 @@
     isNormalUser = true;
     extraGroups = [ "wheel" ];
     shell = pkgs.fish;
-    openssh.authorizedKeys.keys = [
-      "REPLACE_WITH_SINGLE_LINE_PUBLIC_KEY"
-    ];
   };
 
   security.sudo.wheelNeedsPassword = false;