Postgres:
- Set empty string as default for wl_title to match MySQL
- Drop foreign key from wl_user
- Change wl_namespace datatype from SMALLINT to INT to match MySQL/SQLite
- Drop PG-specific indexes and sync them with MySQL
Bug: T230428
Bug: T164898
Change-Id: Ie996b81ca59069443976b90d7bcdce29997d768a