feat: remove deprecated features

Remove following functions:
- vim.lsp.util.extract_completion_items
- vim.lsp.util.get_progress_messages
- vim.lsp.util.parse_snippet()
- vim.lsp.util.text_document_completion_list_to_complete_items
- LanguageTree:for_each_child
- health#report_error
- health#report_info
- health#report_ok
- health#report_start
- health#report_warn
- vim.health.report_error
- vim.health.report_info
- vim.health.report_ok
- vim.health.report_start
- vim.health.report_warn

runtime/lua/vim/lsp/handlers.lua

@@ -3,6 +3,7 @@ local protocol = require('vim.lsp.protocol')
 local ms = protocol.Methods
 local util = require('vim.lsp.util')
 local api = vim.api
+local completion = require('vim.lsp._completion')
 
 --- @type table<string,lsp.Handler>
 local M = {}
@@ -353,7 +354,7 @@ M[ms.textDocument_completion] = function(_, result, _, _)
   local textMatch = vim.fn.match(line_to_cursor, '\\k*$')
   local prefix = line_to_cursor:sub(textMatch + 1)
 
-  local matches = util.text_document_completion_list_to_complete_items(result, prefix)
+  local matches = completion._lsp_to_complete_items(result, prefix)
   vim.fn.complete(textMatch + 1, matches)
 end