chore: remove curl as it's installed by default

https://github.com/NixOS/nixpkgs/blob/nixos-unstable/nixos/modules/config/system-path.nix#L13

docs/en/nixos-with-flakes/nixos-flake-and-module-system.md

@@ -216,7 +216,6 @@ Next, you can reference this flake input data source in `configuration.nix`:
     git
     vim
     wget
-    curl
     # Here, the helix package is installed from the helix input data source
     inputs.helix.packages."${pkgs.system}".helix
   ];

docs/zh/nixos-with-flakes/nixos-flake-and-module-system.md

@@ -206,7 +206,6 @@ helix 的 master 分支。
     git
     vim
     wget
-    curl
     # 这里从 helix 这个 inputs 数据源安装了 helix 程序
     inputs.helix.packages."${pkgs.system}".helix
   ];

docs/zh/nixos-with-flakes/nixos-with-flakes-enabled.md

@@ -29,7 +29,6 @@
     git
     vim
     wget
-    curl
   ];
   # 将默认编辑器设置为 vim
   environment.variables.EDITOR = "vim";