nixos-rebuild: nix flake info -> nix flake metadata

As of
NixOS/nix@66fa1c7,
the `nix flake info` and `nix flake list-inputs` commands were merged into
`nix flake metadata`.

pkgs/os-specific/linux/nixos-rebuild/nixos-rebuild.sh

@@ -295,7 +295,7 @@ fi
 
 # Resolve the flake.
 if [[ -n $flake ]]; then
-    flake=$(nix "${flakeFlags[@]}" flake info --json "${extraBuildFlags[@]}" "${lockFlags[@]}" -- "$flake" | jq -r .url)
+    flake=$(nix "${flakeFlags[@]}" flake metadata --json "${extraBuildFlags[@]}" "${lockFlags[@]}" -- "$flake" | jq -r .url)
 fi
 
 # Find configuration.nix and open editor instead of building.