* ext/readline/readline.c (readline_s_delete_text): remove
  checking "$SAFE == 4".

* ext/readline/readline.c: fix rdoc, remove "Raises SecurityError"
  and add "Raises NotImplementedError".

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42409 b2dd03c8-39d4-4d8f-98ff-823fe69b080e