fix(lang/rust): Remove rust-analyzer from nvim-lspconfig (#2755)

According to the maintainer of `rustaceanvim` (see his comment [here](https://github.com/LazyVim/LazyVim/pull/2198#issuecomment-1999475044)) he says
> To pick up on this: There's a good reason rustaceanvim doesn't automatically pick up a mason.nvim installation. It will most likely be built with a different toolchain than the one your project uses, often leading to discrepancies and subtle bugs.
It's easy to configure rustaceanvim to use mason.nvim if you really want it, but I generally adhere to the YAGNI principle.

I tried locally and the removal of `rust-analyzer` from `nvim-lspconfig` doesn't
seem to have any effect on how `rustaceanvim` behaves.

I propose to remove all instances of `rust-analyzer` from `nvim-lspconfig` to avoid
any possible issues from users that don't have `rust-analyzer` installed
in their toolchain (in this case it would pick up Mason's $PATH I
believe), since they will think that since `rust-analyzer` is installed
by Mason, there shouldn't be a problem and report issues as bugs.

lua/lazyvim/plugins/extras/lang/rust.lua

@@ -98,7 +98,6 @@ return {
     "neovim/nvim-lspconfig",
     opts = {
       servers = {
-        rust_analyzer = {},
         taplo = {
           keys = {
             {
@@ -115,11 +114,6 @@ return {
           },
         },
       },
-      setup = {
-        rust_analyzer = function()
-          return true
-        end,
-      },
     },
   },