[Perf] Flip flag for histogram pipeline

We have already whitelisted enough benchmarks that we want to flip the flag
for all Telemetry benchmarks. system_health was the largest benchmark so we
don't expect to encounter request deadline issues on the perf dashboard
side.

Bug: 744736
Change-Id: I62ce9511a32a56b3eb33bc35bdd6e487f135083f
Reviewed-on: https://chromium-review.googlesource.com/1070219
Commit-Queue: Ethan Kuefner <eakuefner@chromium.org>
Reviewed-by: Emily Hanley <eyaich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#562610}