Migrate build images from dev.gitlab.org to gitlab.com

We seem to be incurring significant egress bandwidth charges
transferring data from dev.gitlab.org, which is in Azure. Our CI runners
pull from the container registry on dev.gitlab.org, which then
communicates with Amazon S3. We should move our images back to
GitLab.com because:

1. Reliability: GitLab.com has a high-availability setup.
2. Cost: Network transfers within Google regions should be cheaper than
crossing cloud providers.