We should only be maintaining one cache bundle per repo, but it turns
out that we've had two in the past due to GoB supporting two different
paths to the repo, and users were getting stale bundles as a result.

This CL fixes things so that we should only get a single bundle per
repo.

Bug: 935084
Change-Id: I0d6713280a2abbc20e35ff87e7be115870dd5140
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1566431Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: Dirk Pranke <dpranke@chromium.org>