GitLab

The Media.Engagement.SessionFinished UKM event has
lots of fields from when we were experimenting. We
should remove these prior to our storage cleanup.

BUG=998685

Change-Id: I87bbd5221d97161e042345e00b778096c3729523
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1775195Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: Becca Hughes <beccahughes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#713295}