This reverts commit bb88492f.

Reason for revert: Broke bot_update: https://logs.chromium.org/logs/infra/buildbucket/cr-buildbucket/8824463357494497185/+/u/bot_update/stdout

Original change's description:
> Use py3 in bot_update and gclient recipe_modules
>
> Recipe-Nontrivial-Roll: build
> Recipe-Nontrivial-Roll: build_limited
> Recipe-Nontrivial-Roll: chrome_release
> Recipe-Nontrivial-Roll: chromiumos
> Recipe-Nontrivial-Roll: infra
> Bug: 1289280
> Change-Id: Id61bacf4acef319f7ea22161081b632677ca363c
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3402082
> Reviewed-by: Yiwei Zhang <yiwzhang@google.com>
> Reviewed-by: Gavin Mak <gavinmak@google.com>
> Commit-Queue: Josip Sokcevic <sokcevic@google.com>

Recipe-Nontrivial-Roll: build
Recipe-Nontrivial-Roll: build_limited
Recipe-Nontrivial-Roll: chrome_release
Recipe-Nontrivial-Roll: chromiumos
Recipe-Nontrivial-Roll: infra
Bug: 1289280
Change-Id: I371d599b17b42edd7b1aae581695e75a80ebae83
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3403476
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>