Stop sanitizing contact information from bridge descriptors

context: https://lists.torproject.org/pipermail/tor-dev/2016-December/011756.html

Why does CollecTor remove ContactInfo from bridge descriptors? Publishing the ContactInfo should not (directly) reveal the bridge location?

use-case for that data: bridge group detection

If plain publishing is not acceptable how about generating a random string replacement for a given ContactInfo string. https://lists.torproject.org/pipermail/tor-dev/2016-December/011761.html

That mapping contactInfo -> random id should remain static for at least 24 hours.