refactor(utils): remove not used function

lua/gopher/_utils/init.lua

@@ -9,17 +9,6 @@ function utils.is_tbl_empty(t)
   return next(t) == nil
 end
 
----@param s string
----@return string
-function utils.rtrim(s)
-  local n = #s
-  while n > 0 and s:find("^%s", n) do
-    n = n - 1
-  end
-
-  return s:sub(1, n)
-end
-
 ---@param msg string
 ---@param lvl any
 function utils.deferred_notify(msg, lvl)