[webaudio] Unstable test names

[jugglinmike]

The webaudio tests define tests whose titles change from one execution to the next. I haven't experienced this when testing locally, but it's apparent in the results collected via Taskcluster and published to wpt.fyi. For example, here's a comparison of results from cors-check.https.html between two consecutive commits to WPT (neither of which modified that file):

@padenot @rtoy I believe these values are expected to vary between executions. Do you think the webaudio's framework can be modified to omit them from the testharness.js test titles?

[gsnedders]

Closing in favour of #12781.