Revert "nixos/profiles/base: install vim w/nix-syntax plugin"

Adding custom plugins causes the `vim` command to be a wrapper script
running `vim -u ...`, which makes it not load the default ~/.vimrc.
(This is analogous to #177375 about neovim.)

As of Vim 9, the syntax-highlighting portion of the nix plugin is
upstream; the full plugin is only needed for indentation etc. (see also
e261eb152b). So, using regular pkgs.vim
works around this behavior/bug and causes any ~/.vimrc to get loaded,
without regressing the syntax highlighting support that motivated the
change being reverted here.

This reverts commit 0b5a0cbc69.

nixos/modules/profiles/base.nix

@@ -19,13 +19,7 @@
     pkgs.cryptsetup # needed for dm-crypt volumes
 
     # Some text editors.
-    (pkgs.vim.customize {
+    pkgs.vim
-      name = "vim";
-      vimrcConfig.packages.default = {
-        start = [ pkgs.vimPlugins.vim-nix ];
-      };
-      vimrcConfig.customRC = "syntax on";
-    })
 
     # Some networking tools.
     pkgs.fuse