Add new perf desktop bots. Remove dcheck_always_on=true for all perf bots. Cleanup some more GYP traces. Remove gn_ prefix for all mixins for readability. BUG=chromium:665874 NOTRY=True Review-Url: https://codereview.webrtc.org/2505183003 Cr-Commit-Position: refs/heads/master@{#15138}