fix(lang.clang): fix clangd_extensions.nvim (#6804)

## Description
`clangd_extensions.nvim` does not seem to take `server` key any more,
which was used to setup the plugin with clangd `cmd`, `init_options`
etc. Instead you only need to configure the clangd server via lspconfig
and the plugin separately according to my understanding.

Remove the unnecessary `opts.setup` which also requires the plugin
itself and loads it and make the plugin lazy-loaded on c/c++ files only.

References:
- https://github.com/p00f/clangd_extensions.nvim#configuration
-
https://github.com/p00f/clangd_extensions.nvim/issues/49#issuecomment-1719654413

PS: I don't do C/C++, so testers would be welcome.
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## Related Issue(s)
Fixes #6800
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  If this PR fixes any issues, please link to the issue here.
  - Fixes #<issue_number>
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## Screenshots

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## Checklist

- [x] I've read the
[CONTRIBUTING](https://github.com/LazyVim/LazyVim/blob/main/CONTRIBUTING.md)
guidelines.

lua/lazyvim/plugins/extras/lang/clangd.lua

@@ -23,8 +23,7 @@ return {
 
   {
     "p00f/clangd_extensions.nvim",
-    lazy = true,
+    ft = { "c", "cpp", "objc", "objcpp" },
-    config = function() end,
     opts = {
       inlay_hints = {
         inline = false,
@@ -94,13 +93,6 @@ return {
           },
         },
       },
-      setup = {
-        clangd = function(_, opts)
-          local clangd_ext_opts = LazyVim.opts("clangd_extensions.nvim")
-          require("clangd_extensions").setup(vim.tbl_deep_extend("force", clangd_ext_opts or {}, { server = opts }))
-          return false
-        end,
-      },
     },
   },