graphqlbackend: Deprecate URI again
Created by: keegancsmith
Edit: This originally also added a fullName field, but we adjusted this PR to just remove URI until we are certain we want a fullName field.
URI is confusing and isn't used yet. Use the more descriptive fullName field. We intentionally do not update the DB type fields yet since that is a larger change. The more important change is how we adjust the user facing API.
Test plan: CI
Related https://github.com/sourcegraph/sourcegraph/pull/3995#pullrequestreview-245954335 and https://github.com/sourcegraph/sourcegraph/issues/4370