This reverts commit cbdf0c1e.

Reason for revert: 
Broke tint bots

From log:
https://logs.chromium.org/logs/tint/buildbucket/cr-buildbucket.appspot.com/8864003131025797600/+/steps/bot_update/0/stdout 

Bot page:
https://ci.chromium.org/p/tint/builders/try/linux-clang-rel-x64/b8864003131025797600?

Original change's description:
> Return HEAD when ref is refs/heads/main
>
> R=​ehmaldonado@chromium.org
>
> Change-Id: I67b40cf48f0f9880e0f055a83d768bbefd704892
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2528118
> Commit-Queue: Josip Sokcevic <sokcevic@google.com>
> Reviewed-by: Dirk Pranke <dpranke@google.com>

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

Bug: 1147494
Change-Id: Ieb21e15161ccc267f5d453a0196b1f0a2b43f366
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2529700Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>