neovim: Drop plenary-nvim

This *shouldn't* be needed since it's a dependency of other vim plugins
and the dependency *should* automatically be handled at the nix level.

home/neovim.nix

@@ -438,10 +438,6 @@ in
           })
         '';
       }
-      {
-        plugin = plenary-nvim;
-        type = "lua";
-      }
       {
         plugin = nvim-autopairs;
         type = "lua";