This reverts commit 19512276.

Reason for revert: broke ART bots.
Bug: 1153114

Original change's description:
> repo: auto-update depot_tools when used
>
> Since gclient automatically syncs this checkout when used,
> have repo do the same for CrOS users.
>
> Bug: 1148984
> Test: ran and saw it auto-update when used externally
> Test: ran and saw it not auto-update when used inside of a repo checkout
> Change-Id: I56b9a45ef3a9ed501f6277e8f8357d4719cf2557
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2537164
> Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
> Reviewed-by: Michael Mortensen <mmortensen@google.com>
> Commit-Queue: Mike Frysinger <vapier@chromium.org>

TBR=vapier@chromium.org,ehmaldonado@chromium.org,mmortensen@google.com,infra-scoped@luci-project-accounts.iam.gserviceaccount.com,mmortensen@chromium.org

Change-Id: Ic0ac9155e3acde87966f518213a5a8440e167295
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1148984
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2560955Reviewed-by: Andrii Shyshkalov <tandrii@google.com>
Commit-Queue: Andrii Shyshkalov <tandrii@google.com>