Thread CPU utilization will always be gathered after Part 2, making the "cpu"
(CPUUtilization) feature redundant. Stop requesting it everywhere it is
currently listed: the about:profiling settings checkbox list, all desktop and
Fenix presets, the devtools perf actor's default feature set, and the
performance test harnesses (mozperftest, raptor, talos, the taskcluster
gecko_profile action, and the Fenix startup-profiling helper). Regenerate the
affected perfdocs.
Differential Revision: https://phabricator.services.mozilla.com/D306737