udp statistics: improve peer client reporting

- fix prometheus peer id prefix reporting
- don't report peer id prefix in html output (current method
  was incorrect and output would become huge)

aquatic_udp/src/workers/statistics/collector.rs

@@ -2,7 +2,6 @@ use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::Arc;
 use std::time::Instant;
 
-use crossbeam_channel::Receiver;
 use hdrhistogram::Histogram;
 use num_format::{Locale, ToFormattedString};
 use serde::Serialize;