We made a mistake and not added resource_providers.can_host to the new DB schema of Placement when Placement was split out of Nova. This patch documents that as can_host is not in the DB model it is safe to drop it from the DB to remove the schema inconsistency. Related-Bug: #1978549 Change-Id: Icfe83313e86969b0b9d34c19b6b82a47d685d4d7