test/t_istream_tee: remove misplaced pool_unref() calls
test/t_istream_tee: remove misplaced pool_unref() calls

Don't reply on TeeIstream to hold the pool reference.

CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy