FEATURE: revert disallowing putting URLs in titles for TL0 users (PR #13970)

This reverts a part of changes introduced by FEATURE: Disallow putting urls in the title for TL-0 users by AndrewPrigorshnev · Pull Request #13947 · discourse/discourse · GitHub

In that PR I:

  1. Disallowed topic feature links for TL-0 users
  2. Additionally, disallowed just putting any URL in topic titles for TL-0 users

Actually, we don’t need the second part. It introduced unnecessary complexity for no good reason. In fact, it tries to do the job that anti-spam plugins (like Akismet plugin) should be doing.

This PR reverts this second change.