Ruby

• thread.c (thread_start_func_2): remove unused code. When
  th->safe_level == 4, th->errinfo never be thrown. So, to
  create new exception makes no sense.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@37963 b2dd03c8-39d4-4d8f-98ff-823fe69b080e