[Sheriff] Revert "PY3 related changes to web tests - 1st iteration"

This reverts commit 1e179f3d.

Reason for revert: Suspicious to be causing a lot of web test-related failures, https://ci.chromium.org/ui/p/chromium/builders/try/linux_layout_tests_layout_ng_disabled/21962/overview

Original change's description:
> PY3 related changes to web tests - 1st iteration
>
> Bug:1197679
>
> Currently, with these changes, it is at a point where tests are picked up and running. But the tests are timing out.
> Will address it in the next iteration.
> Results on PY3 - https://ci.chromium.org/p/chromium/builders/try/linux-blink-rel/52312?
>
> Change-Id: I2b983b287b2df1d160f6efaadda670764e6a38e7
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2787682


> Reviewed-by: Dirk Pranke <dpranke@google.com>
> Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
> Commit-Queue: Preethi Mohan <preethim@google.com>
> Cr-Commit-Position: refs/heads/master@{#872083}

Bug: 1197679
Change-Id: Ie9eaa06628cf337fcf074a1d2c11a1514600600b
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2825694


Auto-Submit: Anatoliy Potapchuk <apotapchuk@chromium.org>
Reviewed-by: Anatoliy Potapchuk <apotapchuk@google.com>
Commit-Queue: Anatoliy Potapchuk <apotapchuk@google.com>
Owners-Override: Anatoliy Potapchuk <apotapchuk@google.com>
Cr-Commit-Position: refs/heads/master@{#872382}