Use Tor's SOCKS USERNAME/PASSWORD event strings

[robgjansen]

New enough versions of Tor should already have export a SOCKS_USERNAME and SOCKS_PASSWORD along with circuit control events.

https://github.com/torproject/tor/blob/e3b1e617ae4850280012c95f40e54acdfc897855/src/feature/control/control_fmt.c#L144-L158

We should

• verify these value are available in circuit control events
• update oniontrace to read those values rather than the USERNAME value from the custom patch in the oniontrace README.
• Assuming the above works, we could remove the custom patch from the README.