Remove old AMP UMA metrics.

With https://chromium-review.googlesource.com/c/chromium/src/+/1512304
landed, we have now migrated to measuring AMP performance without having
to match against hard-coded URLs.

This change removes the old UMA logic with hard-coded URL matching.

Change-Id: I8cd9d5d5491f90b2e3357ed81ba0eadb0ed77732
Bug: 939333
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1618271
Reviewed-by: Annie Sullivan <sullivan@chromium.org>
Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Commit-Queue: Bryan McQuade <bmcquade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661494}
5 files changed