Remove no longer needed startup time histogram

We used this histogram to estimate Butter QPS, but this is no longer
needed.

BUG=975013

Change-Id: Ib56e84b99c2257f290d165218c4db5008e584010
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1665937
Reviewed-by: Robert Kaplow (slow) <rkaplow@chromium.org>
Reviewed-by: Fran├žois Doray <fdoray@chromium.org>
Commit-Queue: Fran├žois Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672218}
2 files changed