test: stop leaking goroutine

[mccutchen]

As part of investigating #72, I tried using uber-go/goleak to detect strangeness with goroutines. It turned up this one leak, but I doubt this is what's causing all of our problems.

[github-actions]

🔥 Run benchmarks comparing 5be7a69 against main:

gh workflow run bench.yaml -f pr_number=74

Note: this comment will update with each new commit.

[mccutchen]

This is the leak, the other change is a drive-by cleanup of unnecessary code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.04%. Comparing base (322a83a) to head (5be7a69).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #74   +/-   ##
=======================================
  Coverage   99.04%   99.04%           
=======================================
  Files           2        2           
  Lines         421      421           
=======================================
  Hits          417      417           
  Misses          2        2           
  Partials        2        2           

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