Experiment: set defaultremote=origin in .gitreview

This repository is slotted for deletion anyhow, so might as well abuse it a
little to see how well it'd work to have 'origin' specified as the default
remote in .gitreview.

Change-Id: Ic3852671167f33298e55101c850ab800b0618ee6
Merge "Experiment: set defaultremote=origin in .gitreview"