perf: don't compute locals on buffer updates

Instead we lazily evaluate them on request.
This allow two things :
    * better performances
    * being sure the locas are up to date

lua/nvim-treesitter.lua

@@ -9,12 +9,6 @@ local M = {}
 -- this is the main interface through the plugin
 function M.setup(lang)
   if parsers.has_parser(lang) then
-    if locals.is_supported(lang) then
-      print("Locals setup for", lang)
-      api.nvim_command(string.format([[
-      autocmd NvimTreesitter FileType %s lua vim.api.nvim_buf_attach(0, true, {on_lines=require'nvim-treesitter.locals'.on_lines})
-      ]], lang))
-    end
   end
 end