Remove nvim-cmp plugin configuration

When opening an R or Quarto file, I would see this message:

> "Please, uninstall cmp-r. It's no longer used."

So I have removed the optional nvim-cmp configuration for R.

This is my first time contributing a change, so I hope this is correct

lua/lazyvim/plugins/extras/lang/r.lua

@@ -47,15 +47,6 @@ return {
       require("r.pdf.generic").open = vim.ui.open
     end,
   },
-  {
-    "hrsh7th/nvim-cmp",
-    optional = true,
-    dependencies = { "R-nvim/cmp-r" },
-    opts = function(_, opts)
-      opts.sources = opts.sources or {}
-      table.insert(opts.sources, { name = "cmp_r" })
-    end,
-  },
   {
     "nvim-treesitter/nvim-treesitter",
     opts = { ensure_installed = { "r", "rnoweb" } },