This CL deletes the duplicated getters and setters
for timeline in Stats panel.

Change-Id: I3a08cfc84e6d099084cb5eeb0e25526a76a891a0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2301930Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Zeynep Cankara <zcankara@google.com>
Cr-Commit-Position: refs/heads/master@{#68895}