Duplicate metrics collector registration attempted resulting in CI failure

Currently there is an (unintentional) edit conflict about whether ..."ptutil digest to e8254c0" should be included in main:

1. It was originally merged by @cohosh at bd04c0f3
2. then reversed at 3c0a0063 as it seems to break continuous integration's unit test with * /builds/tpo/anti-censorship/pluggable-transports/snowflake/broker/snowflake-broker_test.go ; Line 92: - duplicate metrics collector registration attempted
3. @meskio then included it again in e2ba4d35 .