git-cl: Remove unused auth configs.

auth_config is a Rietveld thing, so it's not necessary
in most of the code, except for triggering try bots.

Bug: 1001756
Change-Id: I0f243a297b05a43a61b052ba75c5886556e81b4e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1793018Reviewed-by: Andrii Shyshkalov <tandrii@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>