This reverts commit 856ccef0.

Reason for revert: Probably broke chrome os waterfall

Original change's description:
> bot_update: Don't use gclient sync output and rely on gclient revinfo.
>
> In preparation for skipping gclient sync if there are no DEPS changes.
>
> Bug: 1199853
> Change-Id: Ib9b4ab803bc574a384c661765cee5e4c1de5baae
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2912259
> Reviewed-by: Anthony Polito <apolito@google.com>
> Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>

Bug: 1199853
Change-Id: Ib893704dffc68b02dfa7f977e751e236003b7e0b
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2910949
Auto-Submit: Stephen Martinis <martiniss@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Avi Drissman <avi@chromium.org>
Commit-Queue: Stephen Martinis <martiniss@chromium.org>
Owners-Override: Avi Drissman <avi@chromium.org>