Revert "chrome: run tools/media_engagement_preload/make_dafsa.py in python3"

This reverts commit 07e05386c5d83fb0d428b3a847ee4ddac4b20bfd.

Reason for revert: MediaEngagementAutoplayBrowserTest is failing on mac bots:
https://ci.chromium.org/ui/p/chromium/builders/ci/Mac10.11%20Tests/63046/overview
https://ci.chromium.org/ui/p/chromium/builders/ci/Mac10.12%20Tests/43848/overview

Original change's description:
> chrome: run tools/media_engagement_preload/make_dafsa.py in python3
>
> Fixed: 1210295
> Change-Id: I531f99ba4209086c25157854321e3addf1ce632e
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2903407
> Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
> Reviewed-by: Dirk Pranke <dpranke@google.com>
> Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
> Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#884796}

Change-Id: I4bb812fa3ddbfba0450574edf1e4b8e8d36c01eb
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2909213
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Tim Sergeant <tsergeant@chromium.org>
Owners-Override: Tim Sergeant <tsergeant@chromium.org>
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#884891}