Remove unused src= codec metrics. Mark needed ones as expire=never

We have never and are never likely to have a reason to use the
sample rates or channel layouts. We do want to always maintain what type
of codecs Chrome is seeing, so mark all those as expires_after="never".

BUG=975301

Change-Id: If47db9874cf56c54b8a98c7abf6bfa3783d302ee
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1663193
Auto-Submit: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Steven Holte <holte@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Cr-Commit-Position: refs/heads/master@{#670189}
2 files changed