Revert the portions of #17617 that report all errors when a pull
falls back, and go back to just reporting the last error. This was nice
to have, but causes some UX issues because nonexistent images show
additional "unauthorized" errors.
Keep the part of the PR that handled ENOSPC, as this appears to work
even without tracking multiple errors.
Fixes#19419
Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>