docs(lsp): remove obsolete lsp-extension example (#23346)

This example is made obsolete by the addition of `vim.lsp.start()` and
`vim.fs` (whose use is already documented in `:h lsp-quickstart`).

runtime/doc/lsp-extension.txt

@@ -1,129 +0,0 @@
-*lsp-extension.txt*   LSP Extension
-
-                            NVIM REFERENCE MANUAL
-
-
-The `vim.lsp` Lua module is a framework for building LSP plugins.
-
-  1. Start with |vim.lsp.start_client()| and |vim.lsp.buf_attach_client()|.
-  2. Peek at the API: >vim
-       :lua print(vim.inspect(vim.lsp))
-<  3. See |lsp-extension-example| for a full example.
-
-================================================================================
-LSP EXAMPLE                                            *lsp-extension-example*
-
-This example is for plugin authors or users who want a lot of control. If you
-are just getting started see |lsp-quickstart|.
-
-For more advanced configurations where just filtering by filetype isn't
-sufficient, you can use the `vim.lsp.start_client()` and
-`vim.lsp.buf_attach_client()` commands to easily customize the configuration
-however you please. For example, if you want to do your own filtering, or
-start a new LSP client based on the root directory for working with multiple
-projects in a single session. To illustrate, the following is a fully working
-Lua example.
-
-The example will:
-1. Check for each new buffer whether or not we want to start an LSP client.
-2. Try to find a root directory by ascending from the buffer's path.
-3. Create a new LSP for that root directory if one doesn't exist.
-4. Attach the buffer to the client for that root directory.
-
->lua
-  -- Some path manipulation utilities
-  local function is_dir(filename)
-    local stat = vim.loop.fs_stat(filename)
-    return stat and stat.type == 'directory' or false
-  end
-
-  local path_sep = vim.loop.os_uname().sysname == "Windows" and "\\" or "/"
-  -- Assumes filepath is a file.
-  local function dirname(filepath)
-    local is_changed = false
-    local result = filepath:gsub(path_sep.."([^"..path_sep.."]+)$", function()
-      is_changed = true
-      return ""
-    end)
-    return result, is_changed
-  end
-
-  local function path_join(...)
-    return table.concat(vim.tbl_flatten {...}, path_sep)
-  end
-
-  -- Ascend the buffer's path until we find the rootdir.
-  -- is_root_path is a function which returns bool
-  local function buffer_find_root_dir(bufnr, is_root_path)
-    local bufname = vim.api.nvim_buf_get_name(bufnr)
-    if vim.fn.filereadable(bufname) == 0 then
-      return nil
-    end
-    local dir = bufname
-    -- Just in case our algorithm is buggy, don't infinite loop.
-    for _ = 1, 100 do
-      local did_change
-      dir, did_change = dirname(dir)
-      if is_root_path(dir, bufname) then
-        return dir, bufname
-      end
-      -- If we can't ascend further, then stop looking.
-      if not did_change then
-        return nil
-      end
-    end
-  end
-
-  -- A table to store our root_dir to client_id lookup. We want one LSP per
-  -- root directory, and this is how we assert that.
-  local javascript_lsps = {}
-  -- Which filetypes we want to consider.
-  local javascript_filetypes = {
-    ["javascript.jsx"] = true;
-    ["javascript"]     = true;
-    ["typescript"]     = true;
-    ["typescript.jsx"] = true;
-  }
-
-  -- Create a template configuration for a server to start, minus the root_dir
-  -- which we will specify later.
-  local javascript_lsp_config = {
-    name = "javascript";
-    cmd = { path_join(os.getenv("JAVASCRIPT_LANGUAGE_SERVER_DIRECTORY"), "lib", "language-server-stdio.js") };
-  }
-
-  -- This needs to be global so that we can call it from the autocmd.
-  function check_start_javascript_lsp()
-    local bufnr = vim.api.nvim_get_current_buf()
-    -- Filter which files we are considering.
-    if not javascript_filetypes[vim.api.nvim_buf_get_option(bufnr, 'filetype')] then
-      return
-    end
-    -- Try to find our root directory. We will define this as a directory which contains
-    -- node_modules. Another choice would be to check for `package.json`, or for `.git`.
-    local root_dir = buffer_find_root_dir(bufnr, function(dir)
-      return is_dir(path_join(dir, 'node_modules'))
-      -- return vim.fn.filereadable(path_join(dir, 'package.json')) == 1
-      -- return is_dir(path_join(dir, '.git'))
-    end)
-    -- We couldn't find a root directory, so ignore this file.
-    if not root_dir then return end
-
-    -- Check if we have a client already or start and store it.
-    local client_id = javascript_lsps[root_dir]
-    if not client_id then
-      local new_config = vim.tbl_extend("error", javascript_lsp_config, {
-        root_dir = root_dir;
-      })
-      client_id = vim.lsp.start_client(new_config)
-      javascript_lsps[root_dir] = client_id
-    end
-    -- Finally, attach to the buffer to track changes. This will do nothing if we
-    -- are already attached.
-    vim.lsp.buf_attach_client(bufnr, client_id)
-  end
-
-  vim.api.nvim_command [[autocmd BufReadPost * lua check_start_javascript_lsp()]]
-<
-
- vim:tw=78:ts=8:ft=help:norl: