There is no need to override refs/heads/main to be HEAD. This may not
always be true, there is no benefits of doing so and it doesn't play
well with git_cache which will set HEAD to global default branch.

R=gavinmak@google.com

Bug: 1238084
Recipe-Manual-Change: build_limited
Recipe-Nontrivial-Roll: build
Recipe-Nontrivial-Roll: infra
Change-Id: I21ab3463baaf7f86562ab0c65c06c3ac0962a08c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3088295
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>