Decoy registrar: Use dialer from tapdance dialer instead of its own

[mingyech]

Currently the decoy registrar has its own custom dialer. We also have a the dialer from tapdance.Dialer that is used in other registrars and for the connection, so we might want to change to that for consistancy. Also the decoy registrar is setting the reg.Dialer field while other registrars are reading from it, which is a little confusing.