This paragraph was added 10 years ago in f8dc5db315. Hooks are now
commonly used both in internal (ytdl_hook, auto_profiles) and external
scripts (e.g. https://github.com/mpv-player/mpv/issues?q=mp.add_hook).
They are the only way to handle events synchronously and nobody is just
going to change the API and break all scripts at this point, so remove
the warning.