Add retract to entity builder. (#559) r=rnewman
Add retract to entity builder. (#559) r=rnewman


ncalexan/mentat,mozilla/mentat,ncalexan/mentat,ncalexan/mentat,ncalexan/mentat,ncalexan/mentat,ncalexan/mentat,mozilla/mentat,ncalexan/datomish,mozilla/mentat,mozilla/mentat,mozilla/mentat,mozilla/mentat,ncalexan/datomish