[Benchmarking] Turn down nexus6 webview perf

We're turning off all perf tests on nexus 6 webview. This CL removed the
related setups from the benchmarking codes.

chromium.perf.json is updated by running:
  generate_perf_data

android-pixel2-perf-aab-fyi_timing.json and csv files are updated by running:
  generate_perf_sharding.py update-timing --filter-only

Bug: chromium:1042489
Change-Id: I23dd826c2ec4dbfd1f305e29a4c4fcae5e2ba9bf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2006425
Commit-Queue: Wenbin Zhang <wenbinzhang@google.com>
Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#733077}
8 files changed