shared worker: Delete some expiring histograms.

These are expiring and we're not using them:
* SharedWorker.TimeToScriptLoaded
* SharedWorker.TimeToScriptLoadFailed
* SharedWorker.TimeToDeleted

Bug: 975529
Change-Id: I607ce714af22c84373053271cdc3cec910852e4e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1663484
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Auto-Submit: Matt Falkenhagen <falken@chromium.org>
Commit-Queue: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#671246}
10 files changed