allow committers to abandon CLs of other users This is helpful for cleaning up old CLs where the submitter has disappeared. Change-Id: Iec0011056e648d42aa8c6cf0cc9b4db3cebf673b Reviewed-on: https://chromium-review.googlesource.com/416128 Reviewed-by: Daniel Jacques <[email protected]> Tested-by: Daniel Jacques <[email protected]>