Reland "Remove perf_expectations"

This is a reland of 9d5ef42ab6f3967d19dd687740645ad2fec66ccd

Original change's description:
> Remove perf_expectations
>
> This is a modified reland of [1] with most of the changes to sizes.py reverted.
> Those changes are still used by the perf dashboard so must be kept around for
> the time being.
>
> [1] https://chromium.googlesource.com/chromium/src.git/+/5f552b39961e3b36e018fdd7d3d452526bde2e4f
>
> R=dpranke
> Bug: 572393
> Cq-Include-Trybots: luci.chromium.try:linux_chromium_archive_rel_ng;luci.chromium.try:mac_chromium_archive_rel_ng;luci.chromium.try:win_archive;luci.chromium.try:win_x64_archive;master.tryserver.chromium.android:android_archive_rel_ng
>
> Change-Id: I459387d50f4a328192110c7b75983523a14f787d
> Reviewed-on: https://chromium-review.googlesource.com/c/1255303
> Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
> Reviewed-by: Dirk Pranke <dpranke@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#597614}

R=dpranke
Bug: 572393
Cq-Include-Trybots: luci.chromium.try:linux_chromium_archive_rel_ng;luci.chromium.try:mac_chromium_archive_rel_ng;luci.chromium.try:win_archive;luci.chromium.try:win_x64_archive;master.tryserver.chromium.android:android_archive_rel_ng;master.luci.chromium.try:android_cronet

Change-Id: I19d2e305ff842b61aa518b2a3f4d63a393126981
Reviewed-on: https://chromium-review.googlesource.com/c/1269104
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#597738}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 104673f5cd13a85b0c7313fecf5af63d25f868e2