repo-updater: Drop repo trigger set_repo_name and unused repo columns
Created by: keegancsmith
This trigger was part of a backcompat migration from a long time ago. It was from when we renamed the URI column to Name column. It is no longer needed.
The indexed_revision columns are no longer used.
Test plan: unit tests
Part of https://github.com/sourcegraph/sourcegraph/issues/462 Fixes https://github.com/sourcegraph/sourcegraph/issues/644