Revert "[CodeHealth] Migrate remainder of testing/ to Python3 compatible syntax"

This reverts commit 8defc6c6da91e4b7d7a686b7bb67658d9a5ebe55.

Reason for revert: Makes win-chrome fail:
https://ci.chromium.org/p/chrome/builders/try/win-chrome/4538

Original change's description:
> [CodeHealth] Migrate remainder of testing/ to Python3 compatible syntax
>
> and Pylint2.7, and fix resulting errors.
>
> Bug: 1262363
> Change-Id: I09628427dd4caf9d873f3b489b897054430f8567
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3557490
> Reviewed-by: Ben Pastene <[email protected]>
> Commit-Queue: Joshua Hood <[email protected]>
> Cr-Commit-Position: refs/heads/main@{#996200}

Bug: 1262363
Change-Id: I74384a8cbd77e0db5adbbd5815d54e836472b756
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3607233
Auto-Submit: Sebastien Lalancette <[email protected]>
Reviewed-by: Ben Pastene <[email protected]>
Commit-Queue: Ben Pastene <[email protected]>
Cr-Commit-Position: refs/heads/main@{#996362}
NOKEYCHECK=True
GitOrigin-RevId: 53ef7d3a9b421c2fb8b8831a2f20bfbcc95d1428
2 files changed